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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Radiative Defects in Chloride-Activated CdSe Thin Films

Defect recombination limits wide-gap Se-based chalcogenide devices, yet how chloride activation reshapes radiative pathways remains unclear. Here we show that a 40 min CdCl 2 anneal converts evaporated CdSe from porous nanograins into dense micrometer-scale polycrystals and sharpens the optical band edge, reducing the Urbach energy from 85 to 17 meV at 300 K. Combining temperature- and fluence-dependent photoluminescence (PL), time-resolved PL, hyperspectral mapping, and hybrid-DFT, we resolve three emissive channels and identify their mechanisms. The near-edge band is excitonic at low temperature and evolves into free-carrier emission at elevated temperature. A sub-gap band at E g −0.45 eV requires above-gap carriers and thermally quenches with a 0.16 eV activation energy. A broad ∼1.05 eV infrared band is excited by above- and below-gap photons and retains microsecond lifetimes at room temperature; patial mapping links it to edge-rich microstructure. Calculations suggest selenium-vacancy and cadmium-vacancy−chlorine complexes, pointing to routes to suppress defect-related losses in wide-gap chalcogenide devices.

Abudulimu, Abasi [Univ. of Toledo, OH (United Stat↗
DOE OSTI2020

Materials Data on K2Na3TlO4 by Materials Project

K2Na3TlO4 crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to six O2- atoms to form distorted KO6 octahedra that share corners with two equivalent TlO4 tetrahedra, corners with ten NaO4 tetrahedra, edges with two equivalent KO6 octahedra, edges with two equivalent TlO4 tetrahedra, and edges with four NaO4 tetrahedra. There are a spread of K–O bond distances ranging from 2.84–2.99 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of K–O bond distances ranging from 2.80–3.28 Å. There are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to four O2- atoms to form distorted NaO4 tetrahedra that share corners with four equivalent KO6 octahedra, corners with two equivalent TlO4 tetrahedra, corners with four NaO4 tetrahedra, an edgeedge with one KO6 octahedra, an edgeedge with one TlO4 tetrahedra, and edges with two NaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 26–47°. There are a spread of Na–O bond distances ranging from 2.34–2.41 Å. In the second Na1+ site, Na1+ is bonded to four O2- atoms to form distorted NaO4 tetrahedra that share corners with two equivalent KO6 octahedra, corners with two equivalent TlO4 tetrahedra, corners with four equivalent NaO4 tetrahedra, edges with two equivalent KO6 octahedra, an edgeedge with one TlO4 tetrahedra, and edges with two equivalent NaO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Na–O bond distances ranging from 2.25–2.51 Å. Tl3+ is bonded to four O2- atoms to form TlO4 tetrahedra that share corners with two equivalent KO6 octahedra, corners with six NaO4 tetrahedra, edges with two equivalent KO6 octahedra, and edges with three NaO4 tetrahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Tl–O bond distances ranging from 2.18–2.27 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 7-coordinate geometry to three K1+, three Na1+, and one Tl3+ atom. In the second O2- site, O2- is bonded in a 7-coordinate geometry to three K1+, three Na1+, and one Tl3+ atom. In the third O2- site, O2- is bonded in a 7-coordinate geometry to three K1+, three Na1+, and one Tl3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Sm2As2Se9 by Materials Project

K2Sm2As2Se9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a distorted body-centered cubic geometry to eight Se2- atoms. There are a spread of K–Se bond distances ranging from 3.41–3.64 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of K–Se bond distances ranging from 3.29–3.54 Å. In the third K1+ site, K1+ is bonded to six Se2- atoms to form distorted KSe6 octahedra that share corners with four equivalent SmSe8 hexagonal bipyramids, corners with two equivalent AsSe5 square pyramids, edges with two equivalent SmSe8 hexagonal bipyramids, and edges with two equivalent KSe6 octahedra. There are a spread of K–Se bond distances ranging from 3.28–3.41 Å. There are two inequivalent Sm3+ sites. In the first Sm3+ site, Sm3+ is bonded to eight Se2- atoms to form distorted SmSe8 hexagonal bipyramids that share corners with two equivalent KSe6 octahedra, a cornercorner with one AsSe5 square pyramid, an edgeedge with one KSe6 octahedra, and faces with two equivalent SmSe8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–20°. There are a spread of Sm–Se bond distances ranging from 2.97–3.10 Å. In the second Sm3+ site, Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.97–3.12 Å. There are four inequivalent As5+ sites. In the first As5+ site, As5+ is bonded in a see-saw-like geometry to four Se2- atoms. There are a spread of As–Se bond distances ranging from 2.43–3.01 Å. In the second As5+ site, As5+ is bonded in a 6-coordinate geometry to four Se2- atoms. There are a spread of As–Se bond distances ranging from 2.48–3.09 Å. In the third As5+ site, As5+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.45 Å) and two longer (2.46 Å) As–Se bond lengths. In the fourth As5+ site, As5+ is bonded to five Se2- atoms to form distorted AsSe5 square pyramids that share corners with two equivalent SmSe8 hexagonal bipyramids and corners with two equivalent KSe6 octahedra. The corner-sharing octahedral tilt angles are 91°. There are a spread of As–Se bond distances ranging from 2.46–3.07 Å. There are fifteen inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. The Se–Se bond length is 2.41 Å. In the second Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, one As5+, and one Se2- atom to form a mixture of distorted corner and edge-sharing SeK2Sm2AsSe octahedra. The Se–Se bond length is 2.43 Å. In the third Se2- site, Se2- is bonded in a distorted T-shaped geometry to two Sm3+ and one As5+ atom. In the fourth Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and two Se2- atoms. There are one shorter (2.44 Å) and one longer (3.05 Å) Se–Se bond lengths. In the fifth Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to two K1+ and two As5+ atoms. In the sixth Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent K1+, two equivalent Sm3+, one As5+, and one Se2- atom. In the seventh Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and two Se2- atoms. The Se–Se bond length is 2.41 Å. In the eighth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As trigonal bipyramids that share a cornercorner with one SeK2Sm2AsSe octahedra, corners with two equivalent SeK2Sm2As trigonal bipyramids, and edges with three equivalent SeK2Sm2As square pyramids. The corner-sharing octahedral tilt angles are 9°. In the ninth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As trigonal bipyramids that share edges with two equivalent SeK2Sm2AsSe octahedra and edges with two equivalent SeK2Sm2As square pyramids. In the tenth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As square pyramids that share corners with four equivalent SeK2Sm2AsSe octahedra and edges with two equivalent SeK2Sm2As trigonal bipyramids. The corner-sharing octahedra tilt angles range from 23–27°. In the eleventh Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form a mixture of corner and edge-sharing SeK2Sm2As square pyramids. In the twelfth Se2- site, Se2- is bonded in a 4-coordinate geometry to two Sm3+ and two As5+ atoms. In the thirteenth Se2- site, Se2- is bonded in a 2-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. In the fourteenth Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. In the fifteenth Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KBr by Materials Project

KBr is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K1+ is bonded to six equivalent Br1- atoms to form a mixture of edge and corner-sharing KBr6 octahedra. The corner-sharing octahedral tilt angles are 0°. All K–Br bond lengths are 3.35 Å. Br1- is bonded to six equivalent K1+ atoms to form a mixture of edge and corner-sharing BrK6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KBi2 by Materials Project

KBi2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. K is bonded in a 12-coordinate geometry to twelve equivalent Bi atoms. All K–Bi bond lengths are 3.98 Å. Bi is bonded to six equivalent K and six equivalent Bi atoms to form a mixture of face, edge, and corner-sharing BiK6Bi6 cuboctahedra. All Bi–Bi bond lengths are 3.40 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KLuTa2O7 by Materials Project

KLuTa2O7 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. K1+ is bonded to eight O2- atoms to form KO8 hexagonal bipyramids that share edges with two equivalent KO8 hexagonal bipyramids and edges with six TaO6 octahedra. There are a spread of K–O bond distances ranging from 2.56–2.76 Å. Lu3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Lu–O bond distances ranging from 2.08–2.72 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two equivalent KO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 42°. There is two shorter (1.97 Å) and four longer (2.00 Å) Ta–O bond length. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four equivalent KO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 37–42°. There is two shorter (1.97 Å) and four longer (2.01 Å) Ta–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent K1+ and two equivalent Lu3+ atoms to form distorted corner-sharing OK2Lu2 tetrahedra. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Lu3+ and two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one K1+, one Lu3+, and two Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3IO5 by Materials Project

K3O5I crystallizes in the tetragonal P4/ncc space group. The structure is three-dimensional. there are three inequivalent K sites. In the first K site, K is bonded to five O atoms to form KO5 square pyramids that share corners with five equivalent IO5 square pyramids. There are one shorter (2.55 Å) and four longer (2.64 Å) K–O bond lengths. In the second K site, K is bonded in a distorted body-centered cubic geometry to eight equivalent O atoms. There are four shorter (2.81 Å) and four longer (2.97 Å) K–O bond lengths. In the third K site, K is bonded in a 12-coordinate geometry to twelve O atoms. There are a spread of K–O bond distances ranging from 3.17–3.39 Å. There are two inequivalent O sites. In the first O site, O is bonded to five K and one I atom to form a mixture of distorted edge and corner-sharing OK5I octahedra. The corner-sharing octahedral tilt angles are 8°. The O–I bond length is 1.83 Å. In the second O site, O is bonded in a 6-coordinate geometry to five K and one I atom. The O–I bond length is 1.87 Å. I is bonded to five O atoms to form distorted IO5 square pyramids that share corners with five equivalent KO5 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs2KPdF6 by Materials Project

Cs2KPdF6 is (Cubic) Perovskite-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs is bonded to twelve F atoms to form CsF12 cuboctahedra that share corners with twelve equivalent CsF12 cuboctahedra, faces with six equivalent CsF12 cuboctahedra, faces with four equivalent KF6 octahedra, and faces with four equivalent PdF6 octahedra. There are four shorter (3.25 Å) and eight longer (3.34 Å) Cs–F bond lengths. K is bonded to six F atoms to form KF6 octahedra that share corners with six equivalent PdF6 octahedra and faces with eight equivalent CsF12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.58 Å) and four longer (2.59 Å) K–F bond lengths. Pd is bonded to six F atoms to form PdF6 octahedra that share corners with six equivalent KF6 octahedra and faces with eight equivalent CsF12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.00 Å) and two longer (2.23 Å) Pd–F bond lengths. There are two inequivalent F sites. In the first F site, F is bonded in a distorted linear geometry to four equivalent Cs, one K, and one Pd atom. In the second F site, F is bonded to four equivalent Cs, one K, and one Pd atom to form a mixture of distorted edge and corner-sharing FCs4KPd octahedra. The corner-sharing octahedra tilt angles range from 0–6°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3Al2As3 by Materials Project

K3Al2As3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 5-coordinate geometry to five As3- atoms. There are a spread of K–As bond distances ranging from 3.33–3.52 Å. In the second K1+ site, K1+ is bonded in a 4-coordinate geometry to four As3- atoms. There are a spread of K–As bond distances ranging from 3.41–3.52 Å. In the third K1+ site, K1+ is bonded to five As3- atoms to form KAs5 trigonal bipyramids that share corners with eight equivalent AlAs4 tetrahedra, corners with two equivalent KAs5 trigonal bipyramids, edges with two equivalent AlAs4 tetrahedra, and edges with two equivalent KAs5 trigonal bipyramids. There are a spread of K–As bond distances ranging from 3.35–3.45 Å. Al3+ is bonded to four As3- atoms to form AlAs4 tetrahedra that share corners with two equivalent AlAs4 tetrahedra, corners with four equivalent KAs5 trigonal bipyramids, edges with three equivalent AlAs4 tetrahedra, and an edgeedge with one KAs5 trigonal bipyramid. There are a spread of Al–As bond distances ranging from 2.47–2.60 Å. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to four K1+ and four equivalent Al3+ atoms. In the second As3- site, As3- is bonded in a 7-coordinate geometry to five K1+ and two equivalent Al3+ atoms. In the third As3- site, As3- is bonded in a 7-coordinate geometry to five K1+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2BrCl by Materials Project

KCl(KBr) is Caswellsilverite structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. K1+ is bonded to three equivalent Br1- and three equivalent Cl1- atoms to form a mixture of corner and edge-sharing KBr3Cl3 octahedra. The corner-sharing octahedral tilt angles are 0°. All K–Br bond lengths are 3.32 Å. All K–Cl bond lengths are 3.22 Å. Br1- is bonded to six equivalent K1+ atoms to form BrK6 octahedra that share corners with six equivalent ClK6 octahedra, edges with six equivalent BrK6 octahedra, and edges with six equivalent ClK6 octahedra. The corner-sharing octahedral tilt angles are 2°. Cl1- is bonded to six equivalent K1+ atoms to form ClK6 octahedra that share corners with six equivalent BrK6 octahedra, edges with six equivalent BrK6 octahedra, and edges with six equivalent ClK6 octahedra. The corner-sharing octahedral tilt angles are 2°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP by Materials Project

PK1 is Halite, Rock Salt structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. K1+ is bonded to six equivalent P1- atoms to form a mixture of edge and corner-sharing KP6 octahedra. The corner-sharing octahedral tilt angles are 0°. All K–P bond lengths are 3.36 Å. P1- is bonded to six equivalent K1+ atoms to form a mixture of edge and corner-sharing PK6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KYTa2O7 by Materials Project

KYTa2O7 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. K1+ is bonded to eight O2- atoms to form KO8 hexagonal bipyramids that share edges with two equivalent KO8 hexagonal bipyramids, edges with four equivalent YO8 hexagonal bipyramids, and edges with six TaO6 octahedra. There are two shorter (2.53 Å) and six longer (2.78 Å) K–O bond lengths. Y3+ is bonded to eight O2- atoms to form distorted YO8 hexagonal bipyramids that share edges with two equivalent YO8 hexagonal bipyramids, edges with four equivalent KO8 hexagonal bipyramids, and edges with six TaO6 octahedra. There are a spread of Y–O bond distances ranging from 2.12–2.73 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, edges with two equivalent KO8 hexagonal bipyramids, and edges with four equivalent YO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 41–42°. There are two shorter (1.99 Å) and four longer (2.01 Å) Ta–O bond lengths. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, edges with two equivalent YO8 hexagonal bipyramids, and edges with four equivalent KO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 36–41°. There are two shorter (1.99 Å) and four longer (2.02 Å) Ta–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent K1+ and two equivalent Y3+ atoms to form distorted corner-sharing OK2Y2 tetrahedra. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Y3+ and two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one K1+, one Y3+, and two Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KI by Materials Project

IK1 is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K1+ is bonded to six equivalent I1- atoms to form a mixture of edge and corner-sharing KI6 octahedra. The corner-sharing octahedral tilt angles are 0°. All K–I bond lengths are 3.59 Å. I1- is bonded to six equivalent K1+ atoms to form a mixture of edge and corner-sharing IK6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K4As2Se5 by Materials Project

K4As2Se5 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing KSe6 octahedra. The corner-sharing octahedra tilt angles range from 12–15°. There are a spread of K–Se bond distances ranging from 3.30–3.55 Å. In the second K1+ site, K1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing KSe6 octahedra. The corner-sharing octahedra tilt angles range from 12–20°. There are a spread of K–Se bond distances ranging from 3.36–3.57 Å. In the third K1+ site, K1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing KSe6 octahedra. The corner-sharing octahedra tilt angles range from 8–15°. There are a spread of K–Se bond distances ranging from 3.38–3.42 Å. In the fourth K1+ site, K1+ is bonded to six Se2- atoms to form a mixture of edge and corner-sharing KSe6 octahedra. The corner-sharing octahedra tilt angles range from 8–21°. There are a spread of K–Se bond distances ranging from 3.31–3.81 Å. There are two inequivalent As3+ sites. In the first As3+ site, As3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.37 Å) and two longer (2.38 Å) As–Se bond lengths. In the second As3+ site, As3+ is bonded in a water-like geometry to two Se2- atoms. There are one shorter (2.37 Å) and one longer (2.39 Å) As–Se bond lengths. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five K1+ and one As3+ atom to form SeK5As octahedra that share corners with six SeK5As octahedra, a cornercorner with one SeK4As trigonal bipyramid, edges with nine SeK5As octahedra, and an edgeedge with one SeK4As trigonal bipyramid. The corner-sharing octahedra tilt angles range from 7–96°. In the second Se2- site, Se2- is bonded to five K1+ and one As3+ atom to form distorted SeK5As octahedra that share corners with six SeK5As octahedra, corners with two equivalent SeK4As trigonal bipyramids, edges with seven SeK5As octahedra, and edges with two equivalent SeK4As trigonal bipyramids. The corner-sharing octahedra tilt angles range from 9–96°. In the third Se2- site, Se2- is bonded to five K1+ and one As3+ atom to form distorted SeK5As octahedra that share corners with six SeK5As octahedra, corners with two equivalent SeK4As trigonal bipyramids, and edges with nine SeK5As octahedra. The corner-sharing octahedra tilt angles range from 9–97°. In the fourth Se2- site, Se2- is bonded to five K1+ and one As3+ atom to form distorted SeK5As octahedra that share corners with six SeK5As octahedra, a cornercorner with one SeK4As trigonal bipyramid, edges with seven SeK5As octahedra, and edges with three equivalent SeK4As trigonal bipyramids. The corner-sharing octahedra tilt angles range from 7–97°. In the fifth Se2- site, Se2- is bonded to four K1+ and one As3+ atom to form distorted SeK4As trigonal bipyramids that share corners with six SeK5As octahedra, corners with four equivalent SeK4As trigonal bipyramids, and edges with six SeK5As octahedra. The corner-sharing octahedra tilt angles range from 10–99°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3Pm by Materials Project

K3Pm is beta Cu3Ti-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded to eight equivalent K and four equivalent Pm atoms to form distorted KK8Pm4 cuboctahedra that share corners with four equivalent PmK12 cuboctahedra, corners with fourteen KK8Pm4 cuboctahedra, edges with six equivalent PmK12 cuboctahedra, edges with twelve equivalent KK8Pm4 cuboctahedra, faces with four equivalent PmK12 cuboctahedra, and faces with sixteen KK8Pm4 cuboctahedra. There are a spread of K–K bond distances ranging from 4.23–4.44 Å. There are two shorter (4.31 Å) and two longer (4.33 Å) K–Pm bond lengths. In the second K site, K is bonded to eight K and four equivalent Pm atoms to form distorted KK8Pm4 cuboctahedra that share corners with four equivalent PmK12 cuboctahedra, corners with fourteen KK8Pm4 cuboctahedra, edges with six equivalent PmK12 cuboctahedra, edges with twelve KK8Pm4 cuboctahedra, faces with four equivalent PmK12 cuboctahedra, and faces with sixteen KK8Pm4 cuboctahedra. There are a spread of K–K bond distances ranging from 4.22–4.43 Å. There are two shorter (4.31 Å) and two longer (4.33 Å) K–Pm bond lengths. Pm is bonded to twelve K atoms to form PmK12 cuboctahedra that share corners with six equivalent PmK12 cuboctahedra, corners with twelve KK8Pm4 cuboctahedra, edges with eighteen KK8Pm4 cuboctahedra, faces with eight equivalent PmK12 cuboctahedra, and faces with twelve KK8Pm4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3AlH6 by Materials Project

K3AlH6 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to eight H1- atoms to form distorted KH8 hexagonal bipyramids that share corners with four equivalent KH8 hexagonal bipyramids, edges with six equivalent KH8 hexagonal bipyramids, and edges with four equivalent AlH6 octahedra. There are four shorter (2.60 Å) and four longer (2.95 Å) K–H bond lengths. In the second K1+ site, K1+ is bonded in a linear geometry to two equivalent H1- atoms. Both K–H bond lengths are 2.69 Å. Al3+ is bonded to six H1- atoms to form AlH6 octahedra that share edges with eight equivalent KH8 hexagonal bipyramids. There is four shorter (1.73 Å) and two longer (1.93 Å) Al–H bond length. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded in a distorted trigonal planar geometry to two equivalent K1+ and one Al3+ atom. In the second H1- site, H1- is bonded to five K1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing HK5Al octahedra. The corner-sharing octahedra tilt angles range from 0–15°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K4Ge23 by Materials Project

K4Ge23 crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded in a 8-coordinate geometry to twenty Ge atoms. There are eight shorter (3.55 Å) and twelve longer (3.65 Å) K–Ge bond lengths. In the second K site, K is bonded in a 12-coordinate geometry to twelve Ge atoms. There are eight shorter (3.75 Å) and four longer (3.93 Å) K–Ge bond lengths. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent K and four equivalent Ge atoms to form a mixture of distorted edge and corner-sharing GeK4Ge4 tetrahedra. All Ge–Ge bond lengths are 2.60 Å. In the second Ge site, Ge is bonded in a distorted pentagonal planar geometry to one K and four Ge atoms. There are one shorter (2.52 Å) and three longer (2.56 Å) Ge–Ge bond lengths. In the third Ge site, Ge is bonded in a 7-coordinate geometry to three K and four Ge atoms. The Ge–Ge bond length is 2.64 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Radial pulsations in DB white dwarfs?

Theoretical models of DB white dwarfs are unstable against radial pulsation at effective temperatures near 20,000-30,000 K. Many high-overtone modes are unstable, with periods ranging from 12 s down to the acoustic cutoff period of approximately 0.1 s. The blue edge for radial instability lies at slightly higher effective temperatures than for nonradial pulsations, with the temperature of the blue edge dependent on the assumed efficiency of convection. Models with increased convective efficiency have radial blue edges that are increasingly closer to the nonradial blue edge; in all models the instability persists into the nonradial instability strip. Radial pulsations therefore may exist in the hottest DB stars that lie below the DB gap; the greatest chance for detection would be observations in the ultraviolet. These models also explain why searches for radial pulsations in DA white dwarfs have failed: the efficient convection needed to explain the blue edge for nonradial DA pulsation means that the radial instability strip is 1000 K cooler than found in previous investigations. The multiperiodic nature of the expected pulsations can be used to advantage to identify very low amplitude modes using the uniform spacing of the modes in frequency. This frequency spacing is a direct indicator of the mass of the star.

Kawaler, Steven D.↗