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Dynamic Nuclear Polarization Enhanced 113 Cd Solid-State Nuclear Magnetic Resonance Spectroscopy Reveals CdSe Nanocrystals with Triangular Two-Dimensional Projections are Terminated by {100} Facets

Surface structure plays an important role in particle growth and determining the chemical and photophysical properties of semiconductor nanocrystals (NCs). Therefore, there is a need for structural tools that can characterize and detect different surface facets. Here, we sought to investigate the structure of {111} CdSe facets by applying dynamic nuclear polarization (DNP) enhanced 113 Cd and 77 Se solid-state nuclear magnetic resonance (SSNMR) spectroscopy to zinc-blende CdSe NCs that exhibit triangular two-dimensional (2D) projections within transmission electron microscope (TEM) images. It was originally hypothesized in the literature that these CdSe NCs were tetrahedral in shape and terminated by facets from the {111} family of lattice planes of the zinc-blende structure. Surprisingly, we observe 113 Cd NMR spectra indicating that the primary facets are from the {100} family of lattice planes. We also obtained DNP-enhanced 113 Cd and 77 Se SSNMR spectra of recently reported right trigonal bipyramidal (rTriBP) CdSe NCs grown by seeded growth. The 113 Cd NMR spectra rTriBP CdSe NCs are consistent with {100} surface facets. TEM images show that rTriBP NCs may also exhibit triangular 2D projections that are similar to the so-called tetrahedral NCs. Based upon these results, we conclude that the so-called tetrahedral NCs are predominantly terminated by {100} surface facets and most likely have the same shape as rTriBP NCs. These results highlight the need for multiple complementary techniques when assigning the shape and surface termination of NCs.

Santhiran, Anuluxan [Ames Laboratory (AMES), Ames,↗

20%-efficient polycrystalline Cd(Se,Te) thin-film solar cells with compositional gradient near the front junction

Bandgap gradient is a proven approach for improving the open-circuit voltages (V OC s) in Cu(In,Ga)Se 2 and Cu(Zn,Sn)Se 2 thin-film solar cells, but has not been realized in Cd(Se,Te) thin-film solar cells, a leading thin-film solar cell technology in the photovoltaic market. Here, we demonstrate the realization of a bandgap gradient in Cd(Se,Te) thin-film solar cells by introducing a Cd(O,S,Se,Te) region with the same crystal structure of the absorber near the front junction. The formation of such a region is enabled by incorporating oxygenated CdS and CdSe layers. We show that the introduction of the bandgap gradient reduces the hole density in the front junction region and introduces a small spike in the band alignment between this and the absorber regions, effectively suppressing the nonradiative recombination therein and leading to improved VOCs in Cd(Se,Te) solar cells using commercial SnO 2 buffers. A champion device achieves an efficiency of 20.03% with a V OC of 0.863 V.

14 SOLAR ENERGY↗

Vacancy complexes in Cd 3 As 2

Epitaxial growth of the three-dimensional topological semimetal Cd 3 As 2 on semiconductor substrates enables its use and integration in device applications. Epitaxy also provides an avenue for varying and controlling point defects through modification of the chemical potential during growth. In turn, knowledge of the point defects that are generated in Cd 3 As 2 epilayers will aid the interpretation of electron transport behavior and guide growth efforts to produce material with low defect densities. Point defects in Cd 3 As 2 epilayers grown by molecular beam epitaxy with varying As/Cd flux ratios are probed by positron annihilation spectroscopy. We find that lower As/Cd flux ratios produce higher concentrations of point defects. Remarkably, the measurements indicate that the average defect size is larger than a monovacancy. The data presented here contribute to an evolving picture of vacancy point defects in Cd 3 As 2 and can be used to direct future investigation of the defect-transport relationships in this emerging electronic material.

36 MATERIALS SCIENCE↗

Band Energy Dependence of Defect Formation in the Topological Semimetal Cd3As2

Cadmium Arsenide (Cd3As2) is a prototypical Dirac semimetal that manifests topological properties in a 3D bulk material. In defect-free Cd3As2, the Fermi level lies at a minimum in the density of states at the Dirac point, but experimentally it forms with excess electron carriers and an elevated EF, thereby masking the topological features. To computationally study the self-doping of Cd3As2, we combine density functional theory (DFT) calculations for defect formation energies with quasi-particle self-consistent GW (QSGW) electronic structure calculations. We demonstrate an innate dependence of the point defect formation energies on carrier concentrations and use the QSGW calculated density of states to extrapolate formation energies to arbitrary electron concentrations. This approach allows the quantitative modeling of thermodynamic defect equilibria in topological semimetals and is used to predict how Cd3As2 growth conditions affect the position of EF relative to the Dirac point.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS↗

Exploring the role of high- j configurations in collective observables through the Coulomb excitation of 106 Cd

In this work, the shape and collectivity of 106 Cd was investigated via a sub-barrier-energy Coulomb excitation experiment performed at the NSCL ReA3 facility using the JANUS setup. Transition matrix elements between low-lying states were found to agree with adopted values, and information on the shape and collectivity of higher-lying states was extracted for the first time. Locally-optimized large-scale shell-model calculations were found to describe well the B(E2) transition strengths but failed to reproduce the spectroscopic quadrupole moments Q s . An analysis of the E2 rotational invariants and the normalized quadrupole moment q s indicates that this may be due to a significant degree of triaxiality in 106 Cd which is not captured by the present shell-model calculations. Analogous calculations for the Fe isotopes (two protons below the Z = 28 magic number) reveal the critical role of high-j neutron configurations for the description of quadrupole moments in the heavy Fe and Cd isotopes (two protons below magic Z = 50), but this effect is insufficient to explain the shape of 106 Cd, posing a puzzle for the understanding of nuclear structure towards N = 50.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Doping topological Dirac semimetal with magnetic impurities: Electronic structure of Mn-doped Cd 3 ⁢As 2

The prospect of transforming a Dirac topological semimetal (TSM) into a Weyl TSM phase, following doping by magnetic impurities, is central to TSM applications. The magnetic field from polarized 𝑑 levels of magnetic impurities produces a field with a sharp local structure. To what extent magnetic impurities act in the same manner as an applied field and what are the effects of such a field on the electronic structure of a Dirac TSM are the subject of this paper. We present electronic structure calculations of bulk Cd 3 ⁢As 2 with substitutional doping of Mn impurities in the dilute alloy range. Quasiparticle 𝐺⁡𝑊 (QS⁢𝐺⁡𝑊) ab initio electronic structure calculations are used in conjunction with 𝑘 · 𝑝 model Hamiltonian calculations. As expected, we observe the splitting of the Dirac points into pairs of Weyl points following the doping with Mn. We also show that the electronic structure of Mn-doped Cd 3⁢ As 2 can be emulated by the electronic structure of pristine Cd 3⁢ As 2 with an appropriate external magnetic field. Some properties of the conductivity of bulk Cd 3 ⁢As 2 for different magnetic field orientations are also investigated. Our results inform future opportunities for unique device functionality based on band structure tuning not found in conventional magnetic Weyl TSM.

36 MATERIALS SCIENCE↗

Materials Data on Cd(BO2)2 by Materials Project

Cd(BO2)2 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a 12-coordinate geometry to twelve O2- atoms. There are a spread of Cd–O bond distances ranging from 2.38–2.89 Å. In the second Cd2+ site, Cd2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Cd–O bond distances ranging from 2.22–2.34 Å. There are four inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There is two shorter (1.49 Å) and two longer (1.50 Å) B–O bond length. In the second B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.48–1.51 Å. In the third B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There is one shorter (1.39 Å) and three longer (1.50 Å) B–O bond length. In the fourth B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There is one shorter (1.40 Å) and three longer (1.51 Å) B–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two B3+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two Cd2+ and two B3+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Cd2+ and two B3+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and two B3+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Cd2+ and two B3+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and two B3+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on Cd(NO3)2 by Materials Project

Cd(NO3)2 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cd–O bond distances ranging from 2.35–2.43 Å. In the second Cd2+ site, Cd2+ is bonded in a 7-coordinate geometry to six O2- atoms. There are a spread of Cd–O bond distances ranging from 2.35–2.44 Å. There are four inequivalent N5+ sites. In the first N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. All N–O bond lengths are 1.27 Å. In the second N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.26 Å) and two longer (1.27 Å) N–O bond length. In the third N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.26 Å) and two longer (1.27 Å) N–O bond length. In the fourth N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. All N–O bond lengths are 1.27 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Cd2+ and one N5+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Cd2+ and one N5+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and one N5+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cd2+ and one N5+ atom. In the twelfth O2- site, O2- is bonded in a bent 120 degrees geometry to one Cd2+ and one N5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(CN)2 by Materials Project

Cd(CN)2 is Tungsten structured and crystallizes in the tetragonal P4_2nm space group. The structure is zero-dimensional and consists of two Cd(CN)2 clusters. Cd2+ is bonded in a water-like geometry to two equivalent N3- atoms. Both Cd–N bond lengths are 2.23 Å. C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. N3- is bonded in a linear geometry to one Cd2+ and one C2+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(IO3)2 by Materials Project

Cd(IO3)2 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cd–O bond distances ranging from 2.28–2.42 Å. In the second Cd2+ site, Cd2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Cd–O bond distances ranging from 2.28–2.68 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and two I5+ atoms. There are one shorter (1.86 Å) and one longer (2.73 Å) O–I bond lengths. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cd2+ and one I5+ atom. The O–I bond length is 1.84 Å. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.83 Å. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Cd2+ and one I5+ atom. The O–I bond length is 1.85 Å. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.84 Å. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and one I5+ atom. The O–I bond length is 1.85 Å. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Cd2+ and one I5+ atom. The O–I bond length is 1.86 Å. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and two I5+ atoms. There are one shorter (1.84 Å) and one longer (2.69 Å) O–I bond lengths. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and one I5+ atom. The O–I bond length is 1.86 Å. In the tenth O2- site, O2- is bonded in a distorted single-bond geometry to one Cd2+ and one I5+ atom. The O–I bond length is 1.87 Å. In the eleventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Cd2+ and one I5+ atom. The O–I bond length is 1.89 Å. In the twelfth O2- site, O2- is bonded in a 2-coordinate geometry to one Cd2+ and two I5+ atoms. There are one shorter (1.83 Å) and one longer (2.72 Å) O–I bond lengths. There are four inequivalent I5+ sites. In the first I5+ site, I5+ is bonded in a 6-coordinate geometry to four O2- atoms. In the second I5+ site, I5+ is bonded in a 3-coordinate geometry to four O2- atoms. In the third I5+ site, I5+ is bonded in a 6-coordinate geometry to three O2- atoms. In the fourth I5+ site, I5+ is bonded in a 3-coordinate geometry to four O2- atoms.

36 MATERIALS SCIENCE↗

Materials Data on Cd(HN2)4 by Materials Project

Cd(N2H)4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to six N+0.75- atoms to form corner-sharing CdN6 octahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Cd–N bond distances ranging from 2.36–2.44 Å. In the second Cd2+ site, Cd2+ is bonded to six N+0.75- atoms to form a mixture of edge and corner-sharing CdN6 octahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Cd–N bond distances ranging from 2.32–2.48 Å. There are sixteen inequivalent N+0.75- sites. In the first N+0.75- site, N+0.75- is bonded in a water-like geometry to one Cd2+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. In the second N+0.75- site, N+0.75- is bonded in a distorted water-like geometry to one Cd2+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. In the third N+0.75- site, N+0.75- is bonded in a linear geometry to two N+0.75- atoms. There is one shorter (1.17 Å) and one longer (1.20 Å) N–N bond length. In the fourth N+0.75- site, N+0.75- is bonded in a bent 120 degrees geometry to one Cd2+ and one N+0.75- atom. The N–N bond length is 1.19 Å. In the fifth N+0.75- site, N+0.75- is bonded in a single-bond geometry to one N+0.75- atom. The N–N bond length is 1.17 Å. In the sixth N+0.75- site, N+0.75- is bonded in a linear geometry to two N+0.75- atoms. There is one shorter (1.18 Å) and one longer (1.19 Å) N–N bond length. In the seventh N+0.75- site, N+0.75- is bonded in a bent 120 degrees geometry to one Cd2+ and one N+0.75- atom. The N–N bond length is 1.19 Å. In the eighth N+0.75- site, N+0.75- is bonded in a distorted bent 150 degrees geometry to one Cd2+ and one N+0.75- atom. In the ninth N+0.75- site, N+0.75- is bonded in a single-bond geometry to one N+0.75- atom. In the tenth N+0.75- site, N+0.75- is bonded in a bent 120 degrees geometry to one Cd2+ and one N+0.75- atom. In the eleventh N+0.75- site, N+0.75- is bonded in a linear geometry to two N+0.75- atoms. In the twelfth N+0.75- site, N+0.75- is bonded in a linear geometry to two N+0.75- atoms. The N–N bond length is 1.21 Å. In the thirteenth N+0.75- site, N+0.75- is bonded in a distorted trigonal planar geometry to two equivalent Cd2+ and one N+0.75- atom. In the fourteenth N+0.75- site, N+0.75- is bonded in a distorted water-like geometry to one Cd2+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. In the fifteenth N+0.75- site, N+0.75- is bonded in a trigonal planar geometry to two Cd2+ and one N+0.75- atom. In the sixteenth N+0.75- site, N+0.75- is bonded in a water-like geometry to one Cd2+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. There are eight inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one N+0.75- atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(HO)2 by Materials Project

Cd(OH)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing CdO6 octahedra. The corner-sharing octahedra tilt angles range from 31–64°. There are a spread of Cd–O bond distances ranging from 2.29–2.51 Å. In the second Cd2+ site, Cd2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing CdO6 octahedra. The corner-sharing octahedra tilt angles range from 31–64°. There are a spread of Cd–O bond distances ranging from 2.29–2.51 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to four Cd2+ and one H1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to two Cd2+ and one H1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three Cd2+ and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to three Cd2+ and one H1+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(HO)2 by Materials Project

Cd(OH)2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Cd(OH)2 sheet oriented in the (0, 0, 1) direction. Cd2+ is bonded to six equivalent O2- atoms to form edge-sharing CdO6 octahedra. All Cd–O bond lengths are 2.35 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. O2- is bonded in a single-bond geometry to three equivalent Cd2+ and one H1+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(HO)2 by Materials Project

Cd(OH)2 crystallizes in the monoclinic C2 space group. The structure is two-dimensional and consists of one Cd(OH)2 sheet oriented in the (0, 0, 1) direction. Cd2+ is bonded to six equivalent O2- atoms to form edge-sharing CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.31–2.39 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. O2- is bonded in a distorted single-bond geometry to three equivalent Cd2+ and one H1+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(Bi9O14)2 by Materials Project

CdCd(Bi9O14)4 is Antimony trioxide-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional and consists of one cadmium molecule and one Cd(Bi9O14)4 framework. In the Cd(Bi9O14)4 framework, Cd2+ is bonded in a bent 150 degrees geometry to two O2- atoms. There are one shorter (2.68 Å) and one longer (2.75 Å) Cd–O bond lengths. There are thirty-six inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.20–2.89 Å. In the second Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.71 Å. In the third Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.09–2.89 Å. In the fourth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.20–2.72 Å. In the fifth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–2.73 Å. In the sixth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.15–2.93 Å. In the seventh Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–3.03 Å. In the eighth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.22–2.85 Å. In the ninth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.18–2.85 Å. In the tenth Bi3+ site, Bi3+ is bonded to five O2- atoms to form distorted corner-sharing BiO5 square pyramids. There are a spread of Bi–O bond distances ranging from 2.10–2.68 Å. In the eleventh Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.15–2.85 Å. In the twelfth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.18–3.01 Å. In the thirteenth Bi3+ site, Bi3+ is bonded to five O2- atoms to form distorted corner-sharing BiO5 square pyramids. There are a spread of Bi–O bond distances ranging from 2.16–2.40 Å. In the fourteenth Bi3+ site, Bi3+ is bonded in a distorted square pyramidal geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.16–2.48 Å. In the fifteenth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.23–2.83 Å. In the sixteenth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.16–2.69 Å. In the seventeenth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.21–2.92 Å. In the eighteenth Bi3+ site, Bi3+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Bi–O bond distances ranging from 2.24–2.40 Å. In the nineteenth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.71 Å. In the twentieth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.71 Å. In the twenty-first Bi3+ site, Bi3+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Bi–O bond distances ranging from 2.11–2.51 Å. In the twenty-second Bi3+ site, Bi3+ is bonded in a distorted pentagonal planar geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.25–2.45 Å. In the twenty-third Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–2.46 Å. In the twenty-fourth Bi3+ site, Bi3+ is bonded in a distorted T-shaped geometry to three O2- atoms. There are a spread of Bi–O bond distances ranging from 2.21–2.50 Å. In the twenty-fifth Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Bi–O bond distances ranging from 2.21–2.34 Å. In the twenty-sixth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–2.96 Å. In the twenty-seventh Bi3+ site, Bi3+ is bonded in a distorted square pyramidal geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.18–2.58 Å. In the twenty-eighth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.19–2.74 Å. In the twenty-ninth Bi3+ site, Bi3+ is bonded in a distorted see-saw-like geometry to four O2- atoms. There are a spread of Bi–O bond distances ranging from 2.14–2.67 Å. In the thirtieth Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.16–2.86 Å. In the thirty-first Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.96 Å. In the thirty-second Bi3+ site, Bi3+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.17–2.78 Å. In the thirty-third Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to five O2- atoms. There are a spread of Bi–O bond distances ranging from 2.19–2.98 Å. In the thirty-fourth Bi3+ site, Bi3+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Bi–O bond distances ranging from 2.10–2.91 Å. In the thirty-fifth Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Bi–O bond distances ranging from 2.12–2.74 Å. In the thirty-sixth Bi3+ site, Bi3+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. All Bi–O bond lengths are 2.12 Å. There are fifty-six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the fifth O2- site, O2- is bonded in a distorted T-shaped geometry to three Bi3+ atoms. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to two Bi3+ atoms. In the seventh O2- site, O2- is bonded in a 7-coordinate geometry to five Bi3+ and two O2- atoms. There are one shorter (1.51 Å) and one longer (2.55 Å) O–O bond lengths. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Bi3+ and one O2- atom. The O–O bond length is 1.48 Å. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to three Bi3+ and one O2- atom. The O–O bond length is 1.48 Å. In the twelfth O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to four Bi3+ atoms. In the thirteenth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Bi3+ atoms. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to two Bi3+ and one O2- atom. In the fifteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the sixteenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the seventeenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twentieth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twenty-first O2- site, O2- is bonded to one Cd2+ and three Bi3+ atoms to form distorted corner-sharing OCdBi3 trigonal pyramids. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the twenty-third O2- site, O2- is bonded in a trigonal planar geometry to three Bi3+ and one O2- atom. In the twenty-fourth O2- site, O2- is bonded in a 1-coordinate geometry to three Bi3+ and one O2- atom. In the twenty-fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the twenty-sixth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the twenty-seventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the twenty-eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the twenty-ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the thirtieth O2- site, O2- is bonded in a 2-coordinate geometry to three Bi3+ atoms. In the thirty-first O2- site, O2- is bonded in a 2-coordinate geometry to four Bi3+ atoms. In the thirty-second O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the thirty-third O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the thirty-fourth O2- site, O2- is bonded in a 2-coordinate geometry to four Bi3+ atoms. In the thirty-fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the thirty-sixth O2- site, O2- is bonded to four Bi3+ atoms to form distorted corner-sharing OBi4 tetrahedra. In the thirty-seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Bi3+ and one O2- atom. In the thirty-eighth O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the thirty-ninth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the fortieth O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the forty-first O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the forty-second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the forty-third O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the forty-fourth O2- site, O2- is bonded in a distorted T-shaped geometry to three Bi3+ atoms. In the forty-fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Cd2+ and two Bi3+ atoms. In the forty-sixth O2- site, O2- is bonded in a 2-coordinate geometry to three Bi3+ atoms. In the forty-seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to three Bi3+ atoms. In the forty-eighth O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the forty-ninth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the fiftieth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the fifty-first O2- site, O2- is bonded in a 3-coordinate geometry to two Bi3+ and one O2- atom. The O–O bond length is 1.49 Å. In the fifty-second O2- site, O2- is bonded in a trigonal planar geometry to three Bi3+ atoms. In the fifty-third O2- site, O2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the fifty-fourth O2- site, O2- is bonded in a distorted tetrahedral geometry to three Bi3+ and one O2- atom. In the fifty-fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Bi3+ atoms. In the fifty-sixth O2- site, O2- is bonded in a 3-coordinate geometry to th

36 MATERIALS SCIENCE↗

Materials Data on Cd(PO3)2 by Materials Project

Cd(PO3)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to six O2- atoms to form CdO6 octahedra that share corners with six PO4 tetrahedra and edges with two equivalent CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.23–2.42 Å. In the second Cd2+ site, Cd2+ is bonded to six O2- atoms to form CdO6 octahedra that share corners with six PO4 tetrahedra and edges with two equivalent CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.26–2.32 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three CdO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 31–58°. There are a spread of P–O bond distances ranging from 1.48–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three CdO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 18–60°. There are a spread of P–O bond distances ranging from 1.48–1.61 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to one Cd2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Cd2+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Cd2+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Cd2+ and one P5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cd(GaCl4)2 by Materials Project

Cd(GaCl4)2 crystallizes in the monoclinic Pc space group. The structure is two-dimensional and consists of one Cd(GaCl4)2 sheet oriented in the (0, 1, 0) direction. Cd2+ is bonded to six Cl1- atoms to form CdCl6 octahedra that share corners with two GaCl4 tetrahedra and edges with two GaCl4 tetrahedra. There are a spread of Cd–Cl bond distances ranging from 2.65–2.75 Å. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four Cl1- atoms to form GaCl4 tetrahedra that share a cornercorner with one CdCl6 octahedra and an edgeedge with one CdCl6 octahedra. The corner-sharing octahedral tilt angles are 59°. There are a spread of Ga–Cl bond distances ranging from 2.14–2.26 Å. In the second Ga3+ site, Ga3+ is bonded to four Cl1- atoms to form GaCl4 tetrahedra that share a cornercorner with one CdCl6 octahedra and an edgeedge with one CdCl6 octahedra. The corner-sharing octahedral tilt angles are 59°. There are a spread of Ga–Cl bond distances ranging from 2.14–2.26 Å. There are eight inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Ga3+ atom. In the second Cl1- site, Cl1- is bonded in an L-shaped geometry to one Cd2+ and one Ga3+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Ga3+ atom. In the fourth Cl1- site, Cl1- is bonded in a bent 120 degrees geometry to one Cd2+ and one Ga3+ atom. In the fifth Cl1- site, Cl1- is bonded in an L-shaped geometry to one Cd2+ and one Ga3+ atom. In the sixth Cl1- site, Cl1- is bonded in a bent 120 degrees geometry to one Cd2+ and one Ga3+ atom. In the seventh Cl1- site, Cl1- is bonded in an L-shaped geometry to one Cd2+ and one Ga3+ atom. In the eighth Cl1- site, Cl1- is bonded in an L-shaped geometry to one Cd2+ and one Ga3+ atom.

36 MATERIALS SCIENCE↗

Prediction of alkaline earth metal ion adsorption on goethite for various background electrolytes with the CD-MUSIC model

As water scarcity drives the use of more saline water sources, contaminant fate and transport models must capture the impact of high concentrations of alkaline earth metal ions (AEMs) and background electrolytes in these more complex waters. By utilizing macroscopic adsorption data from various electrolyte systems, a Charge Distribution – Multisite Complexation (CD-MUSIC) model, capable of incorporating electrolyte adsorption, was able to accurately simulate the adsorption behavior of alkaline earth metal ions onto goethite. The modeling effort was guided by previous spectroscopic and surface complexation modeling of alkaline earth metal adsorption and built on previous CD-MUSIC modeling that accounted for changes in crystal face contributions to the surface site density as a function of specific surface area. Further, the model was constrained to consider only two dominant surface complex species for each metal ion adsorption reaction. These two species were selected from 44 possible species through objective curve fitting of single-solute macroscopic adsorption data. While most of the alkaline earth metal surface complexes formed outer-sphere complexes at the goethite surface, an inner-sphere species was utilized for Mg 2+ . With the surface complex species and equilibrium constants obtained from this study, the calibrated model successfully predicted alkaline earth metal ion adsorption over a wide range of solution and surface conditions; the model predictions encompassed a wide range of pH (5–11), solute/solid ratio (1.37 × 10 -5 – 8.33 × 10 -4 mol -solute /g -solid ), ionic strengths (0.01 M – 0.7 M), and background electrolytes (Na + , Cs + , Rb + , Cl - , and NO 3 - ) using the same crystal face contribution methodology for site density, capacitance values, and surface acidity constants adopted for proton and cadmium adsorption in previous work (Han and Katz, 2019). Model simulations for a range of background water chemistries demonstrated the potential for Mg 2+ to reduce Cd 2+ adsorption to goethite in model seawater and oil- and gas-produced waters.

42 ENGINEERING↗