PbFCl Structure Research Articles

The Synthesis and Crystal Structure of Six Quaternary Lithium-Alkaline Earth Metal Alumo-Silicides and Alumo-Germanides, A2LiAlTt2 (A = Mg, Ca, Sr, Ba; Tt = Si, Ge)

Reported are the synthesis and structural characterization of a series of quaternary lithium-alkaline earth metal alumo-silicides and alumo-germanides with the base formula A2LiAlTt2 (A = Ca, Sr, Ba; Tt = Si, Ge). To synthesize each compound, a mixture of the elements with the desired stoichiometric ratio was loaded into a niobium tube, arc welded shut, enclosed in a silica tube under vacuum, and heated in a tube furnace. Each sample was analyzed by powder and single-crystal X-ray diffraction, and the crystal structure of each compound was confirmed and refined from single-crystal X-ray diffraction data. The structures, despite the identical chemical formulae, are different, largely dependent on the nature of the alkaline earth metal. The differing cation determines the structure type—the calcium compounds are part of the TiNiSi family with the Pnma space group, the strontium compounds are isostructural with Na2LiAlP2 with the Cmce space group, and the barium compounds crystallize with the PbFCl structure type in the P4/nmm space group. The anion (silicon or germanium) only impacts the size of the unit cell, with the silicides having smaller unit cell volumes than the germanides.

Chemically Controllable Magnetic Transition Temperature and Magneto‐Elastic Coupling in MnZnSb Compounds

AbstractMagneto‐caloric materials offer the possibility to design environmentally friendlier thermal management devices compared to the widely used gas‐based systems. The challenges to develop this solid‐state based technology lie in the difficulty of finding materials presenting a large magneto‐caloric effect over a broad temperature span together with suitable secondary application parameters such as low heat capacity and high thermal conductivity. A series of compounds derived from the PbFCl structure is investigated using a combination of computational and experimental methods focusing on the change of cell volume in magnetic and non‐magnetic ground states. Scaling analysis of the magnetic properties determines that they are second order phase transition ferromagnets and that the magnetic entropy change is driven by the coupling of magneto‐elastic strain in the square‐net through the magnetic transition determined from neutron and synchrotron X‐ray diffraction. The primary and secondary application related properties are measured experimentally, and the c/a parameter is identified as an accurate proxy to control the magnetic transition. Chemical substitution on the square‐net affords tuning of the Curie temperature over a broad temperature span between 252 and 322 K. A predictive machine learning model for the c/a parameter is developed to guide future exploratory synthesis.

Solvothermal Synthesis and Characterization of Nest-shaped BiOCl

BiOCl with nest morphology was preparation successfully. By the condition that the ratio of BiCl3 to urea is 1:2 and with a simple solvothermal route. The morphology and composition of BiOCl were studied by X-ray diffractometer (XRD), scanning electron microscope (SEM), and UV-vis spectrophotometer methods. SEM result indicates that the sample exhibited nest-shaped structures. XRD results showed that the synthesized sample were pbfcl layered structure BiOCl with good crystallinity. UV–vis spectra reveal that the band gap energy of the BiOCl was 3.57 eV.

Synthesis, Crystal and Electronic Structure of Layered AMSb Compounds (A = Rb, Cs; M = Zn, Cd)

Synthesis, crystal structure, thermal stability, and electronic band structure of four new metal antimonides AMSb (A = Rb, Cs; M = Zn, Cd) are reported. CsZnSb and RbZnSb crystallize in the hexagonal ZrBeSi structure type, in a P63/mmc space group (no. 194, Z = 2) and unit cell dimensions of a = 4.5588(2)/4.5466(4) Å and c = 11.9246(6)/11.0999(10) Å. CsCdSb and RbCdSb crystallize in the tetragonal PbFCl structure type in a P4/nmm space group (no. 129; Z = 2) and unit cell parameters of a = 4.8884(5)/4.8227(3) Å and c = 8.8897(9)/8.5492(7) Å. All four compounds are air‐ and water‐sensitive and are shown through DSC measurements to decompose between 975 K and 1060 K. Analysis of the calculated electronic band structure shows that the Zn‐containing antimonides are topologically trivial narrow bandgap semiconductors, whereas Cd‐containing compounds exhibit a band inversion along Γ‐Z direction.

Layered CeSO and LiCeSO Oxide Chalcogenides Obtained via Topotactic Oxidative and Reductive Transformations.

The chemical accessibility of the CeIV oxidation state enables redox chemistry to be performed on the naturally coinage-metal-deficient phases CeM1- xSO (M = Cu, Ag). A metastable black compound with the PbFCl structure type (space group P4/ nmm: a = 3.8396(1) Å, c = 6.607(4) Å, V = 97.40(6) Å3) and a composition approaching CeSO is obtained by deintercalation of Ag from CeAg0.8SO. High-resolution transmission electron microscopy reveals the presence of large defect-free regions in CeSO, but stacking faults are also evident which can be incorporated into a quantitative model to account for the severe peak anisotropy evident in all the high-resolution X-ray and neutron diffractograms of bulk CeSO samples; these suggest that a few percent of residual Ag remains. A straw-colored compound with the filled PbFCl (i.e., ZrSiCuAs- or HfCuSi2-type) structure (space group P4/ nmm: a = 3.98171(1) Å, c = 8.70913(5) Å, V = 138.075(1) Å3) and a composition close to LiCeSO, but with small amounts of residual Ag, is obtained by direct reductive lithiation of CeAg0.8SO or by insertion of Li into CeSO using chemical or electrochemical means. Computation of the band structure of pure, stoichiometric CeSO predicts it to be a Ce4+ compound with the 4f-states lying approximately 1 eV above the sulfide-dominated valence band maximum. Accordingly, the effective magnetic moment per Ce ion measured in the CeSO samples is much reduced from the value found for the Ce3+-containing LiCeSO, and the residual paramagnetism corresponds to the Ce3+ ions remaining due to the presence of residual Ag, which presumably reflects the difficulty of stabilizing Ce4+ in the presence of sulfide (S2-). Comparison of the behavior of CeCu0.8SO with that of CeAg0.8SO reveals much slower reaction kinetics associated with the Cu1- xS layers, and this enables intermediate CeCu1- xLi xSO phases to be isolated.

Two-Channel Kondo Physics due to As Vacancies in the Layered Compound ZrAs_{1.58}Se_{0.39}.

We address the origin of the magnetic-field-independent -|A|T^{1/2} term observed in the low-temperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs_{1.58}Se_{0.39}, we show that vacancies in the square nets of As give rise to the low-temperature transport anomaly over a wide temperature regime of almost two decades in temperature. This low-temperature behavior is in line with the nonmagnetic version of the two-channel Kondo effect, whose origin we ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As layer with a C_{4} symmetry. The pair-breaking nature of the dynamical defects in the square nets of As explains the low superconducting transition temperature T_{c}≈0.14 K of ZrAs_{1.58}Se_{0.39} compared to the free-of-vacancies homologue ZrP_{1.54}S_{0.46} (T_{c}≈3.7 K). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.

Insight on a novel layered semiconductors: CuTlS and CuTlSe

Single crystals of the ternary copper compounds CuTlS and CuTlSe have been successfully grown from stoichiometric melt by using vertical Bridgman-Stockbarger method. The crystal structure of the both compounds has been determined by powder and single crystal X-Ray diffraction. They crystallize in the PbFCl structure type with two formula units in the tetragonal system, space group P4/nmm, а=3.922(2); c=8.123(6); Z=2 and а=4.087(6); c=8.195(19)Å; Z=2, respectively. The band structure of the reported compounds has been analyzed by means of full-potential linearized augmented plane-wave (FLAPW) method based on the density functional theory (DFT). Both compounds have similar band structures and are narrow-gap semiconductors with indirect band gap. The resistivity measurements agree with a semiconductor behavior although anomalies are observed at low temperature.

Type-II Superconductivity in Ternary Zirconium Pnictide Chalcogenide Single Crystals

Layered Pnictides are proven to be a great reservoir for superconductors in the past and ternary zirconium pnictide chalcogenides of ZrXY-type (X = P, As; Y = S, Se) might be a platform for new superconductors. The superconducting properties of carefully grown (chemical transport reaction) single crystals of ZrP1.54S0.46 with a transition temperature of Tc = 3.5K are investigated. This compound (PbFCl structure type) contains square planar nets: One of the nets is completely occupied (no vacancies) by P, the other one characterized by a random distribution of P and S (full occupation: no vacancies). Besides zero-field-cooling (zfc), field-cooling (fc), and remanent moment (rem) measurements, especially magnetization and ac susceptibility measurements are performed. A nearly ideal type-II behavior with a Ginzburg-Landau parameter κ = 24 is found. The magnetization curves between Bc1 and Bc2 for increasing field are in excellent agreement with theoretical calculations performed by E. H. Brandt based on the Ginzburg-Landau theory. The decreasing branches of the magnetization curves are asymmetric about the field axis indicating weak pinning and also large diamagnetic behavior.

Single-Crystal Structures, Optical Absorptions, and Electronic Distributions of Thorium Oxychalcogenides ThOQ (Q = S, Se, Te)

The compounds ThOS, ThOSe, and ThOTe have been synthesized, and their structures have been determined by means of single-crystal X-ray diffraction methods. All three compounds adopt the PbFCl structure type in the tetragonal space group D(4h)(7) - P4/nmm. More precise crystallographic data have been obtained for ThOS and ThOSe, which had previously only been known from X-ray powder diffraction data. ThOS, ThOSe, and ThOTe are yellow-, orange-, and black-colored, respectively. From single-crystal optical absorption measurements the band gaps are 2.22, 1.65, and 1.45 eV, respectively. Optical band gaps, ionic charges, and densities of states were calculated for the three compounds with the use of Density Functional methods.

Unusual superconductivity up to 49 K in single crystalline R-doped CaFe2As2(Ca122) at ambient with R = rare earth

The discovery in 2008 of the Fe-pnictide and Fe-chalcogenide superconductors has generated immense interest. They crystallize in four different structures, namely, the 1111-phase (RFeAsO, where R = rare earth) with the ZrCuSiAs structure (P4/nmm); the 122-phase (AeFe2As2 and AFe2As2, where Ae = alkaline earth and A = alkaline) with the ThCr2Si2 structure (I4/mmm); the 111-phase (AFeAs, where A = alkaline) with the PbFCl structure (P4/nmm); and the 11-phase (FeSe1-x) with the PbO structure (P4/nmm). The highest Tc’s of these compounds are 57 K, 38 K, 20 K and 10 K for the 1111, 122, 111 and 11 structure classes with different electron or hole- ping at ambient. Until now, no effort has been successful to raise the maximum Tc of Fe-pnictides or -chalcogenides to above the 60’s K as predicted. In view of the unsettled superconducting behavior of Ca122 under pressure, we have investigated the electron-doping effect on Ca122, in contrast to previous studies on the 122 class where only hole-doping has been carried out. We have detected superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starts at ~ 49 K with a low critical field ~ 4 Oe, and the other at ~ 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase observed appears to be filamentary or interfacial in nature. The associated superconducting transition at 49 K behaves as Josephson-Junctioncoupled-like, suggesting the existence of a superconducting phase above 49 K in the R-Ca-Fe-As compound system. The results will be presented and the implications discussed.

The β-polymorph of uranium phosphide selenide

β-UPSe was synthesized from the reaction of U2Se3, P and Se in a CsCl flux in a fused-silica tube. It crystallizes with four formula units in the tetra­gonal space group I4/mmm in the UGeTe structure type. The asymmetric unit comprises one U (site symmetry 4mm), one Se (4mm), and one P (mmm.) atom. The U atom is coordinated in a monocapped square-anti­prismatic arrangement, where the square face is formed by P atoms and the other five vertices are Se atoms. The P site is disordered about a mirror plane, showing half-ocupancy for each of the two resulting P atoms. The title structure is related to that of α-UPSe, which crystallizes with two formula units in the tetra­gonal space group P4/nmm in the PbFCl structure type.

Crystal Chemistry and Physical Properties of the Nonmagnetic Kondo Compound HfAs1.7Se0.2

Single crystals of HfAs(1.7)Se(0.2) are grown by chemical transport reaction and their chemical composition characterized in detail by various analytical methods. Chemical analyses and crystal structure investigations by single-crystal X-ray diffraction as well as powder diffraction with synchrotron radiation reveal a tetragonal PbFCl structure type with strong disorder caused by a significant arsenic deficiency (As(0.9)) on the 2a site and mixed occupancy of the 2c site (As(0.8)Se(0.2)). HfAs(1.7)Se(0.2) is a diamagnetic metal which transforms into a superconducting state at T(c)=0.52 K. Similar to other PbFCl-type arsenide selenides, the title compound displays a magnetic-field-independent -AT(1/2) term in the low-temperature electrical resistivity. This unusual term presumably originates from the electron scattering of structural two-level systems. According to the experimental results, HfAs1.7Se0.2 appears to be a rare example of a nonmagnetic Kondo material.

Phase relations in the Nb-Sb-Si and Nb-Sb-P systems

Phase relations in the systems Nb-Sb-Si (0–70 mol % Sb) and Nb-Sb-P (0–50 mol % P) have been studied by X-ray diffraction, and the 1070-K isothermal sections of their phase diagrams have been constructed. The existence of the compound NbSbSi (PbFCl structure) has been confirmed. Both systems contain a few substitutional solid-solution series: Nb3(Sb,Si) and Nb3(Sb,P) (Cr3Si structure, limiting compositions Nb3Sb0.55Si0.45 and Nb3Sb0.8P0.2), Nb3(Si,Sb) and Nb3(P,Sb) (Ti3P structure, limiting compositions Nb3Si0.6Sb0.4 and Nb3P0.5Sb0.5), Nb(P,Sb) (NbAs structure, limiting composition NbP0.8Sb0.2), and Nb(Si,Sb)2 (CrSi2 structure, limiting composition NbSi1.65Sb0.35). Phase equilibria in related systems are analyzed.

Single-crystal structures of uranium and neptunium oxychalcogenides AnO Q ( An=U, Np; Q=S, Se)

The compounds UOS, UOSe, NpOS, and NpOSe have been synthesized and their structures determined by means of single-crystal X-ray diffraction methods. The results provide more detailed crystallographic information, including more precise interatomic distances, than earlier determinations from powder diffraction data. These isostructural compounds adopt the PbFCl structure type. Each An atom is surrounded by four O and five Q atoms in a distorted monocapped square-antiprismatic arrangement.

A Missing Rare‐Earth Oxide Halide Structure Now Observed For Scandium Oxide Iodide, ScOI

AbstractSingle crystals of ScOI were obtained from the residue of a vacuum sublimation of crude ScI3. The colourless plates crystallize with a new structure type: Monoclinic, C2/m, Z = 8, a = 1933.3(6) pm, b = 386.10(8) pm, c = 722.4(2) pm, β = 93.51(3)°, Vm = 538.2(3) cm3 mol−1. The structure represents a missing link between the YOF/SmSI type variants (CN of the metal ion 4+3, only 36 nets stacked) and the PbFCl and FeOCl structure types (only 44 nets stacked, CN 4+4 and 4+2, respectively). In ScOI there are 44 (Sc, O) and 36 nets (I) stacked such that ScIII has a coordination number of 4+3.

Lutetium(III) oxide bromide, LuOBr

Single crystals of lutetium oxide bromide, LuOBr, were obtained accidentally as a by-product of the reaction of lutetium metal, ruthenium powder and lutetium tribromide, LuBr3, in a sealed tantalum container. As is typical for rare-earth oxide halides of the type REOX (RE = rare-earth metal and X = halogen), LuOBr crystallizes in the tetra­gonal PbFCl structure type (matlockite), where Lu, O and Br are situated on positions with 4mm, \overline{4}m2 and 4mm symmetry, respectively.

Geometric variations and electron localizations in intermetallics: PbFCl type compounds

Abstract The structural relations of the intermetallic compounds Cu2Sb, Mn2Sb, Fe2As, Mn2As, Cr2As, Sc2Sb as well as of YTiSi and ZrSiS, all adopting the PbFCl structure, are discussed. In the course of these investigations, the crystal structures of Mn2Sb, Mn2As and Fe2As have been redetermined and refined from single crystal data. Bandstructures have been calculated in the framework of Density Functional Theory. The bonding properties are compared on the basis of partial densities of states, of the Crystal Orbital Hamilton Population (COHP) and of the Electron Localization Function (ELF). The trend of the d electrons to become more localized with increasing number leads to different bonding conditions in the compounds discussed.

Theoretical study of structural and electronic properties of CaFI

The full potential linearized augmented plane wave (FP-LAPW) method withindensity functional theory is applied to study, for the first time, the structural andelectronic properties of CaFI and to compare them with CaFCl and CaFBr, allcompounds belonging to the tetragonal PbFCl structure group with space groupP4/nmm. We used the generalized gradient approximation (GGA) based on exchange–correlationenergy optimization to calculate the total energy and also the Engel–VoskoGGA formalism, which optimizes the corresponding potential for bandstructure calculations. Ground state properties such as the lattice parameters,c/a ratio, bulk modulus, pressure derivative of the bulk modulus and cohesive energy arecalculated as well as the optimized internal parameters, by relaxing the atomic position in theforce directions. The variations of the calculated interatomic distances and angles betweendifferent atomic bonds are discussed. CaFCl was found to have a direct band gap atΓ whereas CaFBr and BaFI have indirect band gaps. From these computed bands, all threematerials are found to be insulators having band gaps of 6.28, 5.46 and 4.50 eV,respectively. We also calculated the valence charge density and the total density of states atequilibrium volume for each compound. The results are in reasonable agreement with theavailable experimental data.

Structure and physical properties of CeSbTe

The structure of CeSbTe was determined by the Rietveld refinement method using powder X-ray diffraction ( R p =6.22% and wR p =8.74%). CeSbTe adopts the PbFCl structure type and crystallizes in the space group Pnma (No. 62) of the orthorhombic system with Z=4 and a=19.0404(6) Å, b=4.3520(1) Å, c=4.3660(2) Å, V=361.78(2) Å 3. It can be viewed as a layered compound which contains an Sb −1 layer distorted from a perfect square net into zig-zag chains. Both its crystallographic and electronic structure indicate a 2-D character. Based on transport properties and band structure calculations, CeSbTe is a metal with a low carrier concentration. Additionally, it exhibits paramagnetic behavior typical of Ce 3+.

Ionic layered PbFCl-type compounds under high pressure

X-ray diffraction experiments under high pressure have been carried out on BaFCl, BaFBr, and BaFI that belong to the family of layered ionic crystals with the matlockite PbFCl structure. Experiments up to 30 GPa with different pressure transmitting media and different powder proportions were undertaken to determine the anisotropic stress component contribution. The bulk and linear moduli were determined for each compound and structural phase transitions have been observed near 21 and 27 GPa for BaFCl and BaFBr, respectively. The difference in bond strength due to the layered properties of these compounds results in clear differences in compressibilities along the two principal directions, perpendicular and parallel to the ${C}_{4}$ axis of the tetragonal matlockite structure. The anisotropic behavior of the unit-cell parameters observed under compression is attributed to the anisotropic coordination of the highly polarizable halogen anion. This phenomenon created a large static dipole at the halogen and involves an energy contribution that seems to stabilize the layered structure.