Several series of quaternary sulfides RE 3 M 1-x SnS7 (RE = La-Nd; M = Ti-Cu, Cd) were synthesized by direct reaction of the elements at 1000 degrees C and their crystal structures were determined by powder X-ray diffraction, as well as single-crystal X-ray diffraction for many members. Most adopt the noncentrosymmetric La3Mn0.5SiS7-type structure (hexagonal, space group P63) consisting of one-dimensional stacks of Sn-centered tetrahedra and columns of face-sharing M-centered octahedra. With focus placed on the La-containing series La3 M 1-x SnS7, further characterization was performed using X-ray photoelectron and electron paramagnetic spectroscopy. Their optical band gaps ranged from 1.5 to 2.5 eV. Selected members of this series were evaluated for various functional properties. La3Mn0.5SnS7 and La3Cd0.5SnS7 show moderate second harmonic generation at 1800 nm but high laser-induced damage thresholds and improved figures of merit relative to benchmark infrared nonlinear optical materials. La3Fe0.5SnS7 exhibits high photocurrent density suitable for photoelectric energy conversion. La3Ni0.5SnS7 demonstrates electrocatalytic activity for the oxygen evolution reaction in water.

To classify ternary rare-earth silicides REM2Si2 and germanides REM2Ge2 adopting the ThCr2Si2-type structure, a two-dimensional map based on radius ratios and valence electron counts was developed. This map suggested that the transition metal M plays a dominant role, which was confirmed independently by applying a machine learning algorithm called the sure independence screening and sparsifying operator (SISSO) method. In this way, a simple one-dimensional descriptor nvalence/root rho based solely on properties of the metal component M was identified in which ThCr2Si2-type phases are more likely to be formed if this descriptor meets a minimum threshold of 1.68 for silicides and 2.27 for germanides. Although arc-melting is typically used to prepare these compounds, it does not usually afford suitably sized crystals for further characterization. Flux growth of ternary germanides was investigated, with the use of indium yielding crystals of RECo2Ge2 (RE = Ce, Eu, Yb) and other compounds.

High-quality single-crystal ingots of Cs2TeX6 (X = Cl, Br) with dimensions of Ø10 × 40 mm and a mass of 9 g were grown using the vertical Bridgman-Stockbarger method. The solution synthesis method improves the purity of the resulting Cs2TeX6 powders to 99.995% compared to the starting materials (99%) and yields more than 95%. The photoluminescence of Cs2TeX6 was studied in the temperature range 80-280 K. A broad luminescence with a wavelength maximum at 595 nm for Cs2TeCl6, and at 693 nm for Cs2TeBr6, was observed at 80 K. With the temperature increase, the emission maximum of Cs2TeBr6 exhibits a red-shift of 11 nm and the luminescence intensity is completely quenched above 210 K. For Cs2TeCl6, the emission maximum exhibits a red-shift of 14 nm and weak luminescence persists up to room temperature. The proposed luminescence mechanism via self-trapped exciton (STE) emission is supported by strong electron-phonon coupling, as evidenced by the high Huang-Rhys parameters (S = 25 for Cs2TeCl6 and S = 21 for Cs2TeBr6). Raman spectra reveal only four active modes, T2g(1), T2g(2), Eg, and A1g, identified between 49 and 292 cm-1, as well as a four-phonon decay through the Eg mode of Cs2TeCl6.

Metal halide perovskites and related perovskite-inspired materials continue to attract attention for next-generation photovoltaic applications. Compositional synthetic design remains the preferred method for exploring property manipulation and for gaining new insights into material stability and behaviour. This study explores the CsSnxGe1-xBr3 perovskite series to elucidate how composition and preparation method, including solvent, mechanochemical, and high-temperature synthesis, direct the chemical structure and influence optoelectronic properties. Various analytical techniques, including solid-state nuclear magnetic resonance (NMR) spectroscopy, nuclear quadrupole resonance (NQR) spectroscopy, powder X-ray diffraction (XRD), diffuse reflectance spectroscopy, and electron microscopy, have been employed to characterize the local atomic environment, long-range crystallographic structure, morphology, and optical properties of the synthesized CsSnxGe1-xBr3 perovskites. NMR and NQR reveal unique chemical environments and electric field gradients, and how the atomic structure responds to different synthetic conditions across the perovskite system. Paired with long-range diffraction and microscopy-based techniques, these methods provide detailed insight into crystallographic phase, B-site mixing, and domain formation across different compositions and syntheses.

A structural and optoelectronic investigation of Sn-Ge B-site alloyed perovskites across length scales.

Quaternary chalcogenides Cu 2 MTtCh 4 ( M = Zn, Cd; Tt = Si, Ge, Sn; Ch = S, Se) with diamond-like structures, derived from the cubic sphalerite and hexagonal wurtzite prototypes, have been extensively studied for their optoelectronic properties. The site distributions of the metal cations, which are often unclear, can be probed by 63 Cu solid-state nuclear magnetic resonance (NMR) spectroscopy. NMR parameters were extracted through a combination of multifield magic-angle spinning (MAS) and non-spinning experiments to establish structural trends within these compounds. Substitution of S with Se led to lower frequencies for the 63 Cu isotropic chemical shift. In contrast, substitution with heavier tetrels (Si to Ge to Sn) led to higher frequency chemical shifts, which correlate with narrower band gaps. Ambiguities in structural models were resolved by arguments about local symmetry of Cu sites, as examined by their quadrupole coupling parameters. The experimental results were compared with density functional theory (DFT) calculations, performed using r 2 SCAN and PBE functionals. The predicted electric field gradient (EFG) parameters were accurate, though the calculated magnetic shieldings exhibited limitations in these narrow-gap semiconductors. This work provides an analytical 63 Cu NMR spectroscopy method that can rapidly aid in assessing local structures in these diamond-like compounds and related chalcogenides.

Antimonides are attractive candidates for thermoelectric materials, but like other intermetallic compounds, their compositions and structures are not easy to predict, and once predicted, they may be difficult to synthesize. Three new ternary antimonides in the K-Cd-Sb system were discovered through a multifaceted approach that involves (i) use of a machine learning algorithm to pinpoint the compositional regions with low formation energy, (ii) rapid experimental compositional screening aided by the hydride route, and (iii) determination of optimal synthesis temperature from in situ high-temperature powder X-ray diffraction data. Various experimental compositions were screened efficiently through the use of KH instead of elemental K as the starting material, which allows greater compositional control and faster reactions through more rapid diffusion. Furthermore, a simple machine learning model was developed to classify ternary K-containing intermetallics according to denser network vs more open (clathrate, layer, and channel) structures and to identify compositional regions in which phases are likely to adopt open structures. This synergistic approach results in the synthesis of compositionally similar but structurally distinct antimonides: monoclinic K2Cd3Sb4 with a layered structure, tetragonal K3Cd11Sb8 with K+ filling channels in the [CdSb] framework, and hexagonal clathrate-like K3Cd17Sb14 with K+ in the center of 20-vertex polyhedral [CdSb] cages. The compositions of the three K-Cd-Sb compounds are nearly charge-balanced, and their chemical bonding can be rationalized by the Zintl concept. Low-temperature transport property measurements reveal that the electrical resistivity and thermopower change over several orders of magnitude from a semiconductor for hexagonal K3Cd17Sb14 to a heavily doped semiconductor for monoclinic K2Cd3Sb4. All three compounds exhibit low thermal conductivity, attributed to the disordered structures made of heavy Cd and Sb atoms. The strategy presented here can be expanded to other systems for the targeted discovery of new inorganic solids.

Abstract Quaternary chalcogenides Cu2MTtCh4 (M = Zn or Cd; Tt = Si, Ge, or Sn; Ch = S or Se) with diamond-like structures, derived from the cubic sphalerite and hexagonal wurtzite prototypes, have been extensively studied for their optoelectronic properties. The structural assignments for these compounds, which were sometimes unclear, can be addressed by probing the copper sites using 63Cu solid-state nuclear magnetic resonance (NMR) spectroscopy. NMR parameters were extracted through a combination of multifield magic-angle spinning (MAS) and nonspinning experiments to establish structural trends within these compounds. Substitution of S with Se led to lower frequencies for the 63Cu isotropic chemical shift. In contrast, substitution with heavier tetrels (Si to Ge to Sn) led to higher-frequency chemical shifts, which correlate with narrower band gaps. Ambiguities in structural models were resolved by arguments about the local symmetry of Cu sites through quadrupole coupling parameters. The experimental results were compared with density functional theory (DFT) calculations performed using the r2SCAN and PBE functionals. The predicted electric field gradient (EFG) parameters were accurate, although the calculated magnetic shieldings exhibited limitations in these narrow-gap semiconductors. This work provides an analytical 63Cu NMR spectroscopy method that can rapidly aid in assessing local structures in these diamond-like compounds and related chalcogenides.

Tungsten-substituted Na3SbS4 shows enhanced ionic conductivity but the role of sintering treatments is not well understood. The effects of sintering on Na3-xSb1-xWxS4 were examined and found to slightly increase the solubility of W, reduce voids, and possibly increase contact area. Changes in phase composition and morphology play a key role in the performance of Na3-xSb1-xWxS4 electrolytes.

Crystal growth of ternary rare-earth iridium germanides RE-Ir-Ge (RE = Ce, Yb) was investigated in indium flux. These experiments resulted in the formation of two polymorphs of CeIrGe2, termed alpha and (I, as well as Yb4Ir7Ge6 and Yb5Ir4Ge10. Single-crystal X-ray diffraction analysis revealed that alpha-CeIrGe2 adopts the CeNiSi2-type structure (orthorhombic, Cmcm, a = 4.3312(16) & Aring;, b = 17.101(6) & Aring;, c = 4.3803(16) & Aring;, Z = 4) containing zigzag chains of Ge atoms, whereas (I-CeIrGe2 adopts the YIrGe2-type structure (orthorhombic, Immm, a = 4.3842(7) & Aring;, b = 8.8960(14) & Aring;, c = 16.258(3) & Aring;, Z = 8) containing dumbbells of Ge atoms. The structure of Yb4Ir7Ge6 was determined at 296 and 193 K, and confirmed to be the U4Re7Si6-type. Yb5Ir4Ge10 adopts the Sc5Co4Si10-type structure (tetragonal, P4/mbm, a = 12.8799(6) & Aring;, c = 4.2797(2) & Aring;, Z = 2) containing squares and dumbbells of Ge atoms; the structure contracts anisotropically, faster along a than c, upon cooling to 100 K.

Quaternary chalcogenides Cu2 MTtCh 4 (M = Zn or Cd; Tt = Si, Ge, or Sn; Ch = S or Se) with diamond-like structures, derived from the cubic sphalerite and hexagonal wurtzite prototypes, have been extensively studied for their optoelectronic properties. The structural assignments for these compounds, which were sometimes unclear, can be addressed by probing the copper sites using 63Cu solid-state nuclear magnetic resonance (NMR) spectroscopy. NMR parameters were extracted through a combination of multifield magic-angle spinning (MAS) and nonspinning experiments to establish structural trends within these compounds. Substitution of S with Se led to lower frequencies for the 63Cu isotropic chemical shift. In contrast, substitution with heavier tetrels (Si to Ge to Sn) led to higher-frequency chemical shifts, which correlate with narrower band gaps. Ambiguities in structural models were resolved by arguments about the local symmetry of Cu sites through quadrupole coupling parameters. The experimental results were compared with density functional theory (DFT) calculations performed using the r2SCAN and PBE functionals. The predicted electric field gradient (EFG) parameters were accurate, although the calculated magnetic shieldings exhibited limitations in these narrow-gap semiconductors. This work provides an analytical 63Cu NMR spectroscopy method that can rapidly aid in assessing local structures in these diamond-like compounds and related chalcogenides.

Lithium intermetallics with channel structures are of interest for energy storage applications. As a major subset of these intermetallics, ternary tetrelides Li-M-Tt (M = metal; Tt = Si, Ge, Sn) were selected to apply machine learning approaches to predict whether they adopt channel vs nonchannel structures. Through the use of a conventional machine learning method (support vector classifier, SVC) and a more interpretable one (sure independence screening and sparsifying operator, SISSO), models were developed to perform this structural classification. By combining predictions of candidates based on these models with the feasibility of their synthesis based on estimated formation energies, two new series of lithium-containing rare-earth silicides were confirmed to adopt channel structures: LiRESi (RE = Pr, Nd, Tm, Lu) with the hexagonal ZrNiAl-type structure and LiRESi2 (RE = Pr, Nd) with the orthorhombic LiCaSi2-type structure.

To investigate new silver-containing chalcogenides, the quaternary rare-earth sulfides RE2Ag2SnS6 (RE = Nd, Sm, Gd, Tb) were prepared by reactions of the elements at 800 degrees C, with crystals obtained in the presence of KBr flux. They adopt an orthorhombic structure (space group Pnma, a = 11.1620(14)-11.2504(4) & Aring;, b = 3.7877(5)- 3.8639(2) & Aring;, c = 21.190(3)-21.2885(8) & Aring;) consisting of [Ag2SnS6] layers separated by RE atoms. The layers are built up of linear AgS2, triangular AgS3, and octahedral SnS6 units. This structure belongs to the unusual Ce2Yb1.67AgSe6 type but with a different occupation of the metal sites.

Lithium-containing chalcogenides with diamond-like structures are potential candidates for infrared nonlinear optical (NLO) materials because they provide high second harmonic generation (SHG) responses while maintaining large band gaps required for high laser-induced damage thresholds. To evaluate the effects of mixed cations and anions on these optical properties, the complete solid solutions Li2Zn1-x Cd x SnS4, Li2CdSn(S1-y Se y )4, and Li2ZnSn(S1-y Se y )4 were synthesized and structurally characterized by a combination of single-crystal X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy. Li2Zn1-x Cd x SnS4 undergoes structural transitions from space group Pn to Pna21 to Pmn21 as Cd substitutes for Zn, associated with different arrangements of the metal atoms. Li2CdSn(S1-y Se y )4 undergoes a structural transition from Pmn21 to Pna21 as Se substitutes for S. Li2ZnSn(S1-y Se y )4 retains the Pn structure within its entire range. The band gaps are large and direct, remaining relatively constant at 3.0-3.3 eV in Li2Zn1-x Cd x SnS4 upon Cd substitution and decreasing to no lower than 2.0 eV in Li2CdSn(S1-y Se y )4, and Li2ZnSn(S1-y Se y )4 upon Se substitution. The majority of compounds evaluated show modest SHG responses (reaching a maximum of 0.4x AgGaS2) and type-1 phase-matchable behavior at a laser wavelength of 2090 nm, but the trends are irregular. They melt congruently above 800 degrees C.

The first-order Ruddlesden-Popper (RP) phases A(2)BX(4) adopt three structure types that differ in coordination geometry around the B site: T-type (octahedral) and T '-type (square planar), which are most common, and T*type (square pyramidal), which is rare. Especially for RP cuprates A(2)CuO(4-delta), it is not intuitively obvious which structure is preferred depending on the combination of cations occupying the A site. Machine learning models were developed that can separate the T- and T '-type structures among these cuprates with an accuracy of >90 %, provided that the T*-type does not form and the phases can be synthesized. Based on these models, structures were predicted for solid solutions (A ', A '', A")(2)CuO4-delta containing a complex mixture of A cations (A ', A '', A" = Sr, La, Gd, Ho, In, Bi). The predictions were tested by targeting various members of these solid solutions through high-temperature reactions followed by slow cooling. Three samples contained pure RP phases which were confirmed to adopt the predicted structures: T-type for Sr0.4La1.5Ho0.1CuO3.8, and T '-type for Gd1.7Ho0.2Bi0.1CuO4 and La0.4Gd1.2Ho0.4CuO4. Five other samples were mixtures that contained RP phases whose structures (when not T*-type) were correctly identified by a slightly better performing model based on extra randomized trees classifier.

Mixed-anion compounds enable properties to be controlled to a greater degree by chemical substitution than single-anion compounds. La3Si2S8I was investigated as a host to develop phosphors based on solid solutions (La1-xREx)3Si2S8I (RE = Ce, Pr, Tb, Dy, Ho; x = 0-0.33) and (La1-x-yCexREy)3Si2S8I (RE = Tb, Dy; x, y = 0-0.33) that exhibit wide color tunability and white emission. Upon excitation with a 364 nm UV laser source, the phosphors emit through a down-conversion process over a wide visible color gamut. Depending on the RE3+ concentration, the spectra featured broad emission (cyan for Ce3+) or sharp 4f-4f emission peaks (red for Ho3+; green for Tb3+; cyan-green and red for Pr3+; yellow and cyan for Dy3+) which can be fine-tuned to a wider gamut. The cosubstituted (La1-x-yCexREy)3Si2S8I phosphors showed even more intense photoluminescence and wider color palettes within the cyan to green regions (Ce3+-Tb3+) and cool to warm white (Ce3+-Dy3+). The photometric parameters were appropriate for backlighting display and near UV-pumped phosphor-converted white light-emitting diodes (pc-wLEDs). Photoluminescence decay profiles follow biexponential behavior with lifetimes ranging from a few ns (for Ce3+) to 3-450 μs (for other RE3+). Most of the optimized phosphors were moderately stable at 80-100 °C before the onset of thermal quenching effects. They gave absolute quantum yields up to 50%, which are favorable for efficient energy conversion. Prototype pc-wLEDs fabricated from a blend of three phosphors or from single-phase phosphors showed promising performance.

Sodium-containing chalcogenides are attractive candidates for use as solid-state electrolytes; however, their ionic conductivities remain a challenge. Simultaneously applying isovalent and aliovalent substitution can enhance ionic conductivity by generating substantial site disorder and high vacancy concentrations. To elucidate the mechanism that facilitates sodium ion conduction, a series of mixed-pnicogen solid solutions were prepared from the parent ternary sulfides Na3 PnS4 (Pn = P, As, Sb) by high-temperature reactions, including an entropy-driven W-substituted phase, Na3-delta P0.32As0.32Sb0.32W0.04S4 (N-PASS-W). N-PASS-W exhibits a very high ionic conductivity of 10 mS cm-1 and a low activation energy of 0.15 eV. Using PXRD and NMR spectroscopy, an atomic-level model for N-PASS-W was proposed, in which ion hopping occurs over two Na sites within a tetragonal structure (P421 c). Relationships were also established between the structure and ionic conductivities of the other members to evaluate the influence of crystalline phase, cation size, and site disorder.

The mixed chalcogenides La3Ga1.67(S1-xSex)7 form a complete solid solution, with members at increments of x = 0.14 prepared as phase-pure samples. Based on their powder X-ray diffraction (XRD) patterns, the cell volume increases with greater Se substitution, but the cell parameters vary in a nonmonotonic way. Single-crystal XRD studies at room temperature indicated that they adopt noncentrosymmetric hexagonal structures (in space group P63) containing stacks of Ga-centered tetrahedra and stacks of octahedra with partially occupied Ga sites. Strong preferences of S vs Se atoms within three types of chalcogen sites lead to unusual structural changes in the intermediate members of the solid solution and can be understood in terms of the need to satisfy optimum bonding requirements. Structure determination of the selenide end-member La3Ga1.67Se7 at low temperature (100 K) revealed a supercell (in space group P61) with a tripled c-axis characterized by distortions of the partially occupied Ga sites and the coordinating Se atoms, which help relieve bond strain. Two Ga sites in tetrahedral and roughly octahedral geometry were assigned by 71Ga solid-state nuclear magnetic resonance spectroscopy. The experimental optical band gaps vary from 2.6 eV for La3Ga1.67S7 to 2.0 eV for La3Ga1.67Se7.