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DOE OSTI2024

Coexistence of antiferrodistortive and polar order in a superconducting SrTi⁢O 3 film

Strontium titanate (SrTiO 3 ) can exhibit multiple orders, including superconductivity, an antiferrodistortive instability and ferroelectricity. The cooperation or competition between these orders in samples that undergo all three transitions is of great fundamental interest. Here we report scanning transmission electron microscopy imaging of the antiferrodistortive and ferroelectric structural distortions in a compressively strained SrTiO 3 film that was previously shown to become superconducting at ~ 410 mK. The experiments are complemented by first-principles simulations. Unlike the polar ferroelectric phase, which is suppressed by dopants, the antiferrodistortive order is insensitive to the presence of the free carriers. The single domain nature of the antiferrodistortive phase excludes any role of antiferrodistortive domain walls in the superconductivity. Furthermore, a previously reported low temperature resistance anomaly is associated with the ferroelectric transition, not the antiferrodistortive transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Collinear Three-Photon Excitation of a Strongly Forbidden Optical Clock Transition

The 1 𝑆 0 − 3 𝑃 0 clock transition in strontium serves as the foundation for the world’s best atomic clocks and for gravitational wave detector concepts in clock atom interferometry. This transition is weakly allowed in the fermionic isotope 87 Sr but strongly forbidden in bosonic isotopes. Here, we demonstrate coherent excitation of the clock transition in bosonic 88 Sr using a novel collinear three-photon process in a weak magnetic field. We observe Rabi oscillations with frequencies of up to 50 kHz using W/cm 2 laser intensities and Gauss-level magnetic field amplitudes. The absence of nuclear spin in bosonic isotopes offers decreased sensitivity to magnetic fields and optical lattice light shifts, enabling atomic clocks with reduced systematic errors. The collinear propagation of the laser fields permits the interrogation of spatially separated atomic ensembles with common laser pulses, a key requirement for dark matter searches and gravitational wave detection with next-generation quantum sensors.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2023

Otolith 87 Sr / 86 Sr identifies natal origin, movement and life history of Burbot Lota lota in the Kootenai River following 45 years of impoundment

Abstract Hydropower has long been an effective form of renewable energy, but the development of the resource has negatively impacted fishes throughout the world. Formulating recovery plans to mitigate these effects requires a firm understanding of species‐specific provenance, life history and life stage habitat requirements. However, the importance of this information is often only recognised after a substantial population decline, when obtaining it becomes demographically challenging. We provide a case study for this scenario and present a post hoc approach to gain insight into these critical data gaps for Burbot Lota lota in the upper Kootenai River in Montana and British Columbia. The population once supported a robust tribal and recreational harvest but declined following impoundment and these fisheries have remained closed or curtailed for nearly 20 years. The reasons for the decline are unknown and actions to assist recovery have been constrained by limited information regarding natal origin, life history and habitat use. We addressed this issue using strontium isotope ratios ( 87 Sr/ 86 Sr) in otoliths collected over four decades in Lake Koocanusa, the reservoir on the Kootenai River above Libby Dam. Due to the geologic heterogeneity of the basin and resulting variation in water 87 Sr/ 86 Sr, the assignment probability for Burbot to their region of natal origin approached unity. Otolith 87 Sr/ 86 Sr also indicated the population was comprised of mainstem‐ and tributary‐origin forms and their relative abundance changed over time. Mainstem Burbot was most abundant during the 1970s and 2000s, whereas tributary forms dominated between these periods. We suggest ecosystem changes following impoundment contributed to this shift in life history forms and the overall decline of the population. Our findings underscore the need for additional investigations of these impacts to guide restoration efforts.

Dunnigan, James L.↗

DOE OSTI2026

Nanoscale elemental mapping reveals the effect of light and temperature on Gephyrocapsa huxleyi coccoliths

Coccolithophores produce vast quantities of stable calcium carbonate coccoliths, occupying the distinctive position as one of the most productive calcifying organisms on Earth. Gephyrocapsa huxleyi, the most abundant species of coccolithophores across modern oceans, plays an important role in the biological carbon pump and may serve as inspiration for nature-based carbon capture and sequestration technologies. Despite intensive study into G. huxleyi, the biological mechanisms of coccolith synthesis remain unclear. Here, we employ synchrotron X-ray fluorescence to quantitatively map elemental incorporation (calcium, Ca; strontium, Sr; sulfur, S; iron, Fe; and silicon, Si) into G. huxleyi coccoliths at 40-nanometer resolution. Trace elements play a role in determining the thermodynamic stability of coccolith carbonate sequestration and may provide insight into unknown mechanisms of coccolithogenesis. Although the coccolith Sr/Ca ratio has been widely applied as a paleoceanographic proxy, understanding of the Sr/Ca phenomena is limited. Our results confirm that Sr/Ca is temperature dependent but challenge the hypothesis that growth rate is a primary determinant. We find that increased light irradiance led to an ~30% decrease in calcium incorporated into the coccoliths. Surprisingly, X-ray fluorescence spectra and mapping revealed evidence of sulfur, at approximately three times the concentration of Sr, embedded in and around the calcite matrix, suggesting that G. huxleyi coccoliths may play an expanded role in the global sulfur cycle. Here, based on our elemental maps, we postulate that sulfur is active in the intracellular coccolith vesicle and plays a direct role in formation of G. huxleyi coccoliths.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Nanoscale interplay of native point defects near Sr-deficient SrxTiO 3 /SrTiO 3 interfaces

SrTiO 3 has many applications involving interfaces with other materials, but defects that affect the properties of SrTiO 3 films can also play a significant role at its heterointerfaces and even at junctions with nonstoichiometric SrTiO 3 . Depth-resolved cathodoluminescence spectroscopy (DRCLS) combined with systematic cation Sr content reduction in SrxTiO 3 ultrathin films grown on SrTiO 3 showed an interplay of native point defects and electronic structure within the Sr-deficient film and how interplay extends tens of nanometers into the substrate below. Understanding how defects form and affect interface electronic structure during epitaxial growth is central to improving complex oxide devices. Controlling the balance of oxygen vacancy defects with strontium vacancies and other acceptor-like defects can improve control over free carrier densities. Likewise, control over nanoscale defect charge distributions can advance new device features such as two-dimensional hole gases and the performance of existing devices such as ferroelectric tunnel junctions. This study shows how DRCLS directly measures the relative densities and spatial distributions of multiple native defects within and extending away from nanoscale SrxTiO 3 /SrTiO 3 junctions and how their interplay varies with controlled epitaxial growth. In turn, these growth-dependent defect variations can help guide SrTiO 3 epitaxial growth with other complex oxides.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Ion-beam-assisted growth of cesium-antimonide photocathodes

We report on the novel use of a Cs+ ion gun for an ion-beam-assisted molecular-beam-epitaxy (IBA-MBE) method to sequentially deposit Cs-Sb cathodes on room temperature substrates as opposed to the standard technique of thermal evaporation on elevated-temperature substrates. The details of the ultrahigh-vacuum chamber, the Cs+ ion source, and the growth technique are elaborated. The final quantum efficiency (QE) is reasonably good for Cs-Sb cathodes grown on two different substrates—Si (100) and strontium titanate—and is comparable to the QE of cathodes grown using thermal sources. This suggests that IBA-MBE could be a viable alternative to grow alkali-antimonides without substrate heating, paving the way for the growth of epitaxial alkali-antimonides in a more reproducible fashion, which may help improve the efficiency of photon detectors and accelerator applications that use alkali-antimonides as electron sources.

Engineering↗

DOE OSTI2024

Enabling resonant ultrasound spectroscopy in high magnetic fields

Resonant ultrasound spectroscopy (RUS) is a powerful method to determine elastic constants with high accuracy and precision from a single measurement of the mechanical resonances of a sample. Conventionally, the quantitative extraction of elastic moduli with RUS assumes free boundary conditions which can often lead to the adoption of unstable sample positioning between ultrasonic transducers that is incompatible with extreme environments like high magnetic fields. We show that, under specific conditions, introducing a small amount of adhesive between a RUS sample and ultrasonic transducers introduces a perturbation to the free resonance condition which can be accounted for by a simple model. This means elastic constants can be determined to within the uncertainty of conventional RUS, but with significant improvements including sample stability and control of sample orientation. We demonstrate the efficacy of this approach with measurements on a range of materials including room temperature measurements on polycrystalline metals, temperature-dependent measurements of the structural phase transition in strontium titanate single crystals, and magnetic field-dependent measurements of magnetic phase transitions in gadolinium polycrystals up to 14 T.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Fossil records of early solar irradiation and cosmolocation of the CAI factory: A reappraisal

Calcium-aluminum–rich inclusions (CAIs) in meteorites carry crucial information about the environmental conditions of the nascent Solar System prior to planet formation. Based on models of 50V– 10 Be co-production by in-situ irradiation, CAIs are considered to have formed within ~0.1 AU from the proto-Sun. Here, we present vanadium (V) and strontium (Sr) isotopic co-variations in fine- and coarse-grained CAIs and demonstrate that kinetic isotope effects during partial condensation and evaporation best explain V isotope anomalies previously attributed to solar particle irradiation. We also report initial excesses of 10 Be and argue that CV CAIs possess essentially a homogeneous level of 10 Be, inherited during their formation. Based on numerical modeling of 50V–10Be co-production by irradiation, we show that CAI formation during protoplanetary disk build-up likely occurred at greater heliocentric distances than previously considered, up to planet-forming regions (~1AU), where solar particle fluxes were sufficiently low to avoid substantial in-situ irradiation of CAIs.

58 GEOSCIENCES↗

DOE OSTI2024

Observation of millihertz-level cooperative Lamb shifts in an optical atomic clock

Collective couplings of atomic dipoles to a shared electromagnetic environment produce a wide range of many-body phenomena. We report on the direct observation of resonant electric dipole-dipole interactions in a cubic array of atoms in the many-excitation limit. The interactions produce spatially dependent cooperative Lamb shifts when spectroscopically interrogating the millihertz-wide optical clock transition in strontium-87. We show that the ensemble-averaged shifts can be suppressed below the level of evaluated systematic uncertainties for optical atomic clocks. Additionally, we demonstrate that excitation of the atomic dipoles near a Bragg angle can enhance these effects by nearly an order of magnitude compared with nonresonant geometries. Our work demonstrates a platform for precise studies of the quantum many-body physics of spins with long-range interactions mediated by propagating photons.

Science & Technology - Other Topics↗

DOE OSTI2021

Partitioning maternal and exogenous diet contributions to otolith 87 Sr/ 86 Sr in kokanee salmon ( Oncorhynchus nerka )

Strontium isotopes ( 87 Sr/ 86 Sr) recorded in the otoliths of Pacific salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith 87 Sr/ 86 Sr over embryonic development in kokanee salmon (Oncorhynchus nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith 87 Sr/ 86 Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87 Sr/ 86 Sr between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Furthermore, understanding how these factors affect otolith 87 Sr/ 86 Sr could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

Evidence that Surface-Segregated Sr Phases Can Be Removed in LSCF via Ceria Pre-Infiltration, Are Less Apt to Form in SSC

Here Ce 0.9 Gd 0.1 O 1.95−x (GDC) pre-infiltration was performed on 12 vol.% La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3−x (LSCF) or Sm 0.5 Sr 0.5 CoO 3−x (SSC) infiltrated GDC Solid Oxide Fuel Cell cathodes. The addition of 7.5 vol.% of ∼40 nm diameter GDC nanoparticles into a ∼30 μ m thick porous scaffold of partially-sintered, sub-micron GDC particles before LSCF infiltration 1) lowered the temperature needed to produce a LSCF-GDC polarization resistance ( R P ) of 0.1 Ohm*cm 2 by ∼50 °C, and 2) reduced the amount of 500 h, 650 °C open-circuit LSCF-GDC R P degradation from ∼37% to ∼6%. In contrast, GDC pre-infiltration had no effect on the initial SSC-GDC R P or the 19% in R P degradation observed during 500 h of 650 °C open-circuit aging. X-Ray Photoelectron Spectroscopy showed that GDC pre-infiltration lowered the concentration of strontium species on the surface of the initial and 650 °C-aged LSCF-GDC, but had no effect on the initial or aged SSC-GDC Sr concentrations. Similarly, Electrochemical Impedance Spectroscopy showed that for both the initial and aged LSCF-GDC, GDC pre-infiltration improved oxygen exchange at the infiltrate-backbone and infiltrate-gas interfaces, but had no effect on the SSC-GDC. Hence, GDC pre-infiltration was concluded to improve LSCF-GDC performance and durability by scavenging exsolved Sr-rich secondary phases that form on the interfaces of LSCF, but not SSC.

36 MATERIALS SCIENCE↗

DOE OSTI2021

The Impact of Sintering Atmosphere and Temperature on the Phase Evolution of High Surface Area LSCF Prepared by In Situ Carbon Templating

The thermochemical stability of lanthanum strontium cobalt ferrite (LSCF) processed between 1000 °C–1200 °C via the in situ carbon templating method was studied. This method generates high surface area ceramics at traditional solid oxide fuel cell (SOFC) sintering temperatures by generating a carbon template in situ and subsequently removing the template by oxidation at 700 °C. Argon processed samples produced an amorphous carbon template, whereas nitrogen tended to form graphitic carbon. Prior to the oxidation step, nitrogen samples comprised larger La 2 O 3 crystallites (22–40 nm) compared to argon (9–17 nm). Upon oxidation, argon samples resulted in a pure LSCF phase with surface areas in the 21–29 m 2 ·g −1 range, whereas nitrogen samples contained significant impurities. This demonstrates that the size of La 2 O 3 crystallites formed during inert processing limited the ability to produce a pure LSCF phase. Symmetrical cells comprising nano-LSCF electrodes generated by the templating method were compared to cells sintered directly in air. Impedance results suggest that nano-LSCF cells and cells processed in air were dominated by interfacial charge transfer resistance and gas diffusion, respectively. The results map out conditions for preparing and integrating high surface area, nanostructured LSCF into SOFC electrodes at traditional sintering temperatures. Strategies for improving the interfacial resistance of nano-LSCF electrodes are discussed.

Muhoza, Sixbert P. (ORCID:0000000299864241)↗

DOE OSTI2024

Radiation Modeling of Z1: Validation of a Novel Radioisotope System

This paper presents the development of a radiation model for a novel strontium-90 (Sr-90) radioisotope heat source developed by Zeno Power Systems (Zeno), which demonstrates a groundbreaking fuel and shielding design that significantly reduces weight compared to traditional concepts. A Monte Carlo N-Particle (MCNP) model has been created to assess the effectiveness of this fuel and shielding design, however validation of the MCNP model is desired. Zeno has developed a prototype device (Z1) to aid in this model validation effort. This project is a collaborative effort between Zeno, the University of Dayton Research Institute (UDRI) and Pacific Northwest National Laboratory (PNNL), where the Z1 prototype was constructed and characterized.

RTG↗

DOE OSTI2022

Ultra-low loss visible light waveguides for integrated atomic, molecular, and quantum photonics

Atomic, molecular and optical (AMO) visible light systems are the heart of precision applications including quantum, atomic clocks and precision metrology. As these systems scale in terms of number of lasers, wavelengths, and optical components, their reliability, space occupied, and power consumption will push the limits of using traditional laboratory-scale lasers and optics. Visible light photonic integration is critical to advancing AMO based sciences and applications, yet key performance aspects remain to be addressed, most notably waveguide losses and laser phase noise and stability. Additionally, a visible light integrated solution needs to be wafer-scale CMOS compatible and capable of supporting a wide array of photonic components. While the regime of ultra-low loss has been achieved at telecommunication wavelengths, progress at visible wavelengths has been limited. Here, we report the lowest waveguide losses and highest resonator Qs to date in the visible range, to the best of our knowledge. We report waveguide losses at wavelengths associated with strontium transitions in the 461 nm to 802 nm wavelength range, of 0.01 dB/cm to 0.09 dB/cm and associated intrinsic resonator Q of 60 Million to 9.5 Million, a decrease in loss by factors of 6x to 2x and increase in Q by factors of 10x to 1.5x over this visible wavelength range. Additionally, we measure an absorption limited loss and Q of 0.17 dB/m and 340 million at 674 nm. This level of performance is achieved in a wafer-scale foundry compatible Si 3 N 4 platform with a 20 nm thick core and TEOS-PECVD deposited upper cladding oxide, and enables waveguides for different wavelengths to be fabricated on the same wafer with mask-only changes per wavelength. These results represent a significant step forward in waveguide platforms that operate in the visible, opening up a wide range of integrated applications that utilize atoms, ions and molecules including sensing, navigation, metrology and clocks.

Chauhan, Nitesh↗

DOE OSTI2020

Mid-infrared frequency doubling using strip-loaded silicon nitride on epitaxial barium titanate thin film waveguides

Broadband mid-infrared (mid-IR) frequency doubling was demonstrated using nonlinear barium titanate (BTO) thin films. The device has a strip-loaded waveguide structure consisting of top silicon nitride (SiN) strips and an underneath BTO guiding layer. The epitaxial BTO was deposited on a strontium titanate (STO) substrate by pulsed-laser deposition. Through a SiN grating coupler, the pumping mid-IR light at wavelength λ = 3.30 − 3.45 µ m was coupled into the nonlinear BTO layer, where the spectrum of the near-infrared (NIR) second-harmonic generation was characterized. The developed BTO waveguides provide a platform for mid-IR nonlinear integrated photonics and on-chip quantum optics.

42 ENGINEERING↗

DOE OSTI2026

Data for "Depth of nutrient uptake by deep-rooted plants is regulated by water availability"

The data set consists of strontium (Sr) isotope ratios (87Sr/86Sr), water isotopes, soil cation concentrations, soil water potential sensor data, and results of 87Sr/86Sr mixing model. The plant canopy size files include the dataset of canopy dimension of sagebrush, lupine, and sunflower. The soil and plant ICPMS (Inductively Coupled Plasma Mass Spectrometry) data file includes both of 87Sr/86Sr, and cation concentration dataset from soil exchangeable pool, apatite pool, silicate extract, atmospheric rain deposition, and plant leaf and stem tissues. The plant dendrochronology file includes the dendrochronogical ring width of several sagebrush, and dendrochemical sample data includes the 87Sr/86Sr for each separated growth ring. The modeling result gives the proportion of nutrient sources of each plants (based on their 87Sr/86Sr in leaf tissues and growth rings) from atmospheric deposition and mineral weathering. Soil water potential data includes continuous collection of soil water potential dataset at 2 depths (30 cm and 60 cm, from Nov 24 - Jun 25) of the sampling site. All the samples were collected from 2 sampling campaign June and July 2023, and rain water is a separate sampling from Aug - Sept 2023, at north-facing hillslope near pumphouse site. The data showed that the depth of cation nutrient acquisition is thus tightly coupled with, and likely determined by, water availability in soil, saprolite and bedrock. The enhanced uptake of cations and water from regions of mineral weathering could confer plant and ecosystem resilience during low water years and may impact the rate of bedrock weathering and watershed chemistry during drought. This dataset includes a file-level metadata (flmd.csv) file that lists each file contained in the dataset with associated metadata; a data dictionary (dd.csv) file that contains column/row headers used throughout the files along with a definition, units, and data type; a location metadata file (locations.csv); and a samples metadata file (samples.csv). All files are provided as comma-separated values (CSV) files (.csv). This work was supported by the Watershed Function Science Focus Area at Lawrence Berkeley National Laboratory funded by the US Department of Energy, Office of Science, Biological and Environmental Research under Contract No. DE-AC02-05CH11231.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2021

Effect of additives on carbon dioxide uptake and compressive strength of dry-cast concrete

The main thrust of the work reported herein is to study the effect of chemical additives to make beneficial use of carbon dioxide in enhancing the compressive strength of dry-cast concrete. The additives used in this investigation were calcium and magnesium oxides and silicates, nickel oxide, sodium hydroxide, sodium bicarbonate and strontium chloride. The experimental results showed that both the carbonation reactions and the compressive strength of dry-cast concrete mixtures were improved when using chemical additives. Experimental investigations for optimisation were also undertaken with selected additives to further increase the carbon dioxide uptake and improve the compressive strength. The best results were obtained when using calcium silicate in combination with calcium oxide. The early-age compressive strength of specimens made from the optimised mixture increased from 9·82 MPa to 13·32 MPa, and the specimens’ carbon dioxide uptake increased from 8·76% to 10·62% of cement weight.

Construction & Building Technology↗

DOE OSTI2020

Materials Data on Sr3Pr10Al12Si18(N2O)18 by Materials Project

Sr(SrPr5Al6Si9(N2O)9)2 is Chalcostibite-derived structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional and consists of two strontium molecules and one SrPr5Al6Si9(N2O)9 framework. In the SrPr5Al6Si9(N2O)9 framework, Sr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Sr–N bond distances ranging from 2.62–3.10 Å. There are a spread of Sr–O bond distances ranging from 2.65–3.09 Å. There are six inequivalent Pr sites. In the first Pr site, Pr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.55–3.09 Å. There are a spread of Pr–O bond distances ranging from 2.43–3.13 Å. In the second Pr site, Pr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.55–3.05 Å. There are a spread of Pr–O bond distances ranging from 2.41–3.10 Å. In the third Pr site, Pr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.53–3.11 Å. There are a spread of Pr–O bond distances ranging from 2.40–3.17 Å. In the fourth Pr site, Pr is bonded in a 2-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.53–3.11 Å. There are a spread of Pr–O bond distances ranging from 2.42–3.18 Å. In the fifth Pr site, Pr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.55–3.07 Å. There are a spread of Pr–O bond distances ranging from 2.42–3.13 Å. In the sixth Pr site, Pr is bonded in a 5-coordinate geometry to five N and five O atoms. There are a spread of Pr–N bond distances ranging from 2.55–3.05 Å. There are a spread of Pr–O bond distances ranging from 2.47–3.10 Å. There are seven inequivalent Al sites. In the first Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two equivalent AlN3O tetrahedra and corners with five SiN4 tetrahedra. There is two shorter (1.83 Å) and one longer (1.88 Å) Al–N bond length. The Al–O bond length is 1.80 Å. In the second Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two equivalent AlN3O tetrahedra and corners with five SiN3O tetrahedra. There is two shorter (1.84 Å) and one longer (1.88 Å) Al–N bond length. The Al–O bond length is 1.81 Å. In the third Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two AlN3O tetrahedra and corners with five SiN4 tetrahedra. There are a spread of Al–N bond distances ranging from 1.83–1.89 Å. The Al–O bond length is 1.80 Å. In the fourth Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two AlN3O tetrahedra and corners with five SiN4 tetrahedra. There is two shorter (1.84 Å) and one longer (1.87 Å) Al–N bond length. The Al–O bond length is 1.79 Å. In the fifth Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two AlN3O tetrahedra and corners with five SiN4 tetrahedra. There are a spread of Al–N bond distances ranging from 1.83–1.88 Å. The Al–O bond length is 1.80 Å. In the sixth Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two AlN3O tetrahedra and corners with five SiN4 tetrahedra. There is two shorter (1.83 Å) and one longer (1.88 Å) Al–N bond length. The Al–O bond length is 1.80 Å. In the seventh Al site, Al is bonded to three N and one O atom to form AlN3O tetrahedra that share corners with two AlN3O tetrahedra and corners with five SiN3O tetrahedra. There is two shorter (1.83 Å) and one longer (1.89 Å) Al–N bond length. The Al–O bond length is 1.80 Å. There are eleven inequivalent Si sites. In the first Si site, Si is bonded to four N atoms to form SiN4 tetrahedra that share corners with two SiN3O tetrahedra and corners with four AlN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.72–1.74 Å. In the second Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN4 tetrahedra. There is one shorter (1.74 Å) and two longer (1.75 Å) Si–N bond length. The Si–O bond length is 1.66 Å. In the third Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN4 tetrahedra. There is one shorter (1.73 Å) and two longer (1.75 Å) Si–N bond length. The Si–O bond length is 1.67 Å. In the fourth Si site, Si is bonded to four N atoms to form SiN4 tetrahedra that share corners with two equivalent SiN3O tetrahedra and corners with four AlN3O tetrahedra. There is two shorter (1.72 Å) and two longer (1.74 Å) Si–N bond length. In the fifth Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN3O tetrahedra. There is one shorter (1.73 Å) and two longer (1.75 Å) Si–N bond length. The Si–O bond length is 1.66 Å. In the sixth Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN3O tetrahedra. There is one shorter (1.72 Å) and two longer (1.76 Å) Si–N bond length. The Si–O bond length is 1.65 Å. In the seventh Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.73–1.76 Å. The Si–O bond length is 1.67 Å. In the eighth Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN4 tetrahedra. There is two shorter (1.74 Å) and one longer (1.76 Å) Si–N bond length. The Si–O bond length is 1.66 Å. In the ninth Si site, Si is bonded to four N atoms to form SiN4 tetrahedra that share corners with two SiN3O tetrahedra and corners with four AlN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.72–1.74 Å. In the tenth Si site, Si is bonded to four N atoms to form SiN4 tetrahedra that share corners with two SiN3O tetrahedra and corners with four AlN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.72–1.74 Å. In the eleventh Si site, Si is bonded to three N and one O atom to form SiN3O tetrahedra that share corners with three AlN3O tetrahedra and corners with three SiN3O tetrahedra. There is one shorter (1.73 Å) and two longer (1.75 Å) Si–N bond length. The Si–O bond length is 1.66 Å. There are twenty-one inequivalent N sites. In the first N site, N is bonded in a 4-coordinate geometry to one Pr, one Al, and two Si atoms. In the second N site, N is bonded in a trigonal planar geometry to one Pr, two Al, and one Si atom. In the third N site, N is bonded in a 2-coordinate geometry to three Pr and two Si atoms. In the fourth N site, N is bonded in a 2-coordinate geometry to one Sr, two Pr, and two Si atoms. In the fifth N site, N is bonded in a 2-coordinate geometry to one Sr, two Pr, and two Si atoms. In the sixth N site, N is bonded to one Pr, one Al, and two Si atoms to form distorted NPrAlSi2 trigonal pyramids that share corners with two OPr4 tetrahedra and corners with two NPrAlSi2 trigonal pyramids. In the seventh N site, N is bonded in a trigonal planar geometry to one Sr, two Al, and one Si atom. In the eighth N site, N is bonded to one Pr, one Al, and two Si atoms to form distorted NPrAlSi2 tetrahedra that share a cornercorner with one NPrAlSi2 tetrahedra, corners with two OSrPr3 tetrahedra, and a cornercorner with one NSrAlSi2 trigonal pyramid. In the ninth N site, N is bonded in a 2-coordinate geometry to one Sr, two Pr, and two Si atoms. In the tenth N site, N is bonded in a trigonal planar geometry to one Pr, two Al, and one Si atom. In the eleventh N site, N is bonded in a trigonal planar geometry to one Pr, two Al, and one Si atom. In the twelfth N site, N is bonded to one Pr, one Al, and two Si atoms to form distorted NPrAlSi2 tetrahedra that share a cornercorner with one NPrAlSi2 tetrahedra, corners with two OPr4 tetrahedra, and a cornercorner with one NSrAlSi2 trigonal pyramid. In the thirteenth N site, N is bonded to one Sr, one Al, and two Si atoms to form distorted NSrAlSi2 trigonal pyramids that share corners with two NPrAlSi2 tetrahedra and corners with two OSrPr3 tetrahedra. In the fourteenth N site, N is bonded in a trigonal planar geometry to one Pr, two Al, and one Si atom. In the fifteenth N site, N is bonded in a 2-coordinate geometry to three Pr and two Si atoms. In the sixteenth N site, N is bonded in a 2-coordinate geometry to three Pr and two Si atoms. In the seventeenth N site, N is bonded in a 2-coordinate geometry to three Pr and two Si atoms. In the eighteenth N site, N is bonded to one Pr, one Al, and two equivalent Si atoms to form distorted NPrAlSi2 trigonal pyramids that share corners with two equivalent OSrPr3 tetrahedra and corners with two equivalent NPrAlSi2 trigonal pyramids. In the nineteenth N site, N is bonded to one Pr, one Al, and two equivalent Si atoms to form distorted NPrAlSi2 trigonal pyramids that share corners with two equivalent OPr4 tetrahedra. In the twentieth N site, N is bonded in a trigonal planar geometry to one Pr, two equivalent Al, and one Si atom. In the twenty-first N site, N is bonded in a trigonal planar geometry to one Pr, two equivalent Al, and one Si atom. There are ten inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to three Pr, one Al, and one Si atom. In the second O site, O is bonded in a 2-coordinate geometry to three Pr, one Al, and one Si atom. In the third O site, O is bonded in a 2-coordinate geometry to one Sr, two Pr, one Al, and one Si atom. In the fourth O site, O is bonded to four Pr atoms to form distorted OPr4 tetrahedra that share corners with two NPrAlSi2 tetrahedra, corners with four OPr4 tetrahedra, and corners with two NPrAlSi2 trigonal pyramids. In the fifth O site, O is bonded to one Sr and three Pr atoms to form distorted OSrPr3 tetrahedra that share a cornercorner with one NPrAlSi2 tetrahedra, corners with four OPr4 tetrahedra, and corners with two NSrAlSi2 trigonal pyramids. In the sixth O site, O is bonded in a 2-coordinate geometry to one Sr, two Pr, one Al, and one Si atom. In the seventh O site, O is bonded in a 2-coordinate geometry to three Pr, one Al, and one Si atom. In the eighth O site, O is bonded in a 2-coordinate geometry to one Sr, two Pr, one Al, and one Si atom. In the ninth O site, O is bonded in a 2-coordinate geometry to three Pr, one Al, and one Si atom. In the tenth O site, O is bonded to one Sr and three Pr atoms to form OSrPr3 tetrahedra that share a cornercorner with one NPrAlSi2 tetrahedra, corners with four OPr4 tetrahedra, and corners with two NSrAlSi2 trigonal pyramids.

36 MATERIALS SCIENCE↗