Space Group Cmcm Research Articles

Ac conductivity and modulus behavior of K0.12Na0.54Ag0.34Nb4AsO13 compound

Some physical properties of K0.12Na0.54Ag0.34Nb4AsO13 powder, synthesized visa a solid-state reaction at 800 °C, are discussed in this study. The vibrational analysis verifies the existence of the AsO43− and NbO67− functional groups. The X-ray powder diffraction pattern and Rietveld refinement confirm the formation of a pure phase that crystallizes in an orthorhombic system with a Cmcm space group. The structure and chemical composition of the compound are studied using the Scanning Electron Microscopy and the Energy Dispersive Spectroscopy. Complex impedance spectroscopy is used to examine the electrical conductivity, dielectric properties and relaxation behavior of the aforementioned compound at different temperatures and across the 0.01 kHz–13 MHz frequency range. The correlation between K0.12Na0.54Ag0.34Nb4AsO13's crystalline structure and its ionic conductivity is also studied.

Chenowethite, Mg(H2O)6[(UO2)2(SO4)2(OH)2]·5H2O, a New Mineral with Uranyl-Sulfate Sheets from Red Canyon, Utah, USA

The new mineral chenowethite, Mg(H2O)6[(UO2)2(SO4)2(OH)2]·5H2O, was found in efflorescence crusts on tunnel walls at the Blue Lizard, Green Lizard and Markey uranium mines in Red Canyon, San Juan County, Utah, USA. The crystals are long, thin blades up to about 0.5 mm long, occurring in irregular sprays and subparallel groups. Chenowethite is pale green yellow. It has white streak, vitreous to silky luster, brittle tenacity, splintery and stepped fracture and two cleavages: {010} perfect and {001} good. It has a hardness (Mohs) of about 2 and is nonfluorescent in both long- and short-wave ultraviolet illumination. The density is 3.05(2) g/cm3. Optically, crystals are biaxial (−) with α = 1.530(2), β = 1.553(2) and γ = 1.565(2) (white light). The 2V is 72(2)° and dispersion is r > v (slight). The optical orientation is X = b, Y = a, Z = c and the mineral exhibits weak pleochroism in shades of pale green yellow: X < Y < Z. The Raman spectrum is consistent with the presence of UO22+, SO42− and OH–/H2O. The empirical formula from electron microprobe analysis and arranged in accordance with the structure is (Mg0.71Fe2+0.09Co0.05Ni0.04)∑0.89(H2O)6[(UO2)2(SO4)2(OH)2]·[(H2O)4.78(NH4)0.22]∑5.00. Chenowethite is orthorhombic, space group Cmcm; the unit-cell parameters are a = 6.951(2), b = 19.053(6), c = 16.372(5) Å, V = 2168.19(7) Å3 and Z = 4. The crystal structure of chenowethite (R1 = 0.0396 for 912 I > 2σI reflections) contains [(UO2)2(SO4)2(OH)2]2− sheets that are topologically equivalent to those in deliensite, feynmanite, greenlizardite, johannite, meitnerite and plášilite.

Magnesium and barium in two substructures: BaTMg2 (T = Pd, Ag, Pt, Au) and the isotypic cadmium compound BaAuCd2 with MgCuAl2 type structure

Abstract The intermetallic barium compounds BaTMg2 (T = Pd, Ag, Pt, Au) and BaAuCd2 were synthesized by reactions of the elements in sealed tantalum ampoules in muffle furnaces. The five compounds crystallize with the orthorhombic MgCuAl2 type structure, space group Cmcm, with small differences in chemical bonding between the magnesium and cadmium series. All samples were characterized through their Guinier powder diffraction patterns. The structures of BaPdMg2 (a = 444.57(4), b = 1174.67(10), c = 827.58(7) pm, wR2 = 0.0460, 475 F 2 values, 16 variables), BaAuMg2 (a = 450.27(6), b = 1183.94(16), c = 838.76(11) pm, wR2 = 0.0355, 473 F 2 values, 16 variables) and BaAuCd2 (a = 463.31(5), b = 1112.79(12), c = 826.63(8) pm, wR2 = 0.0453, 469 F 2 values, 16 variables) were refined from single crystal X-ray diffraction data. The large barium atoms push the [TMg2] respectively [AuCd2] substructures apart. This allows fast moisture attack and leads to fast hydrolyzes of the samples when they get in contact with water. The influence of the difference in electronegativity between magnesium and cadmium is reflected for the pair of compounds BaAuMg2 and BaAuCd2. The magnesium compound shows the higher auridic character, while the cadmium compound shows a tendency towards a three-dimensional cadmium substructure.

Temperature and pressure dependence of the Yb valence state in YbMn∼0.17Si∼1.89

Single crystals of the non-stoichiometric YbMn∼0.17Si∼1.89 intermetallic compound were investigated by room-temperature x-ray diffraction as well as by temperature and pressure-dependent x-ray absorption experiments at the Yb L3 edge. The crystal structure can be described in the orthorhombic space group Cmcm or in the non-centrosymmetric P21 monoclinic space group. In both cases, the cell comprises two Yb sites of identical multiplicity with close coordination numbers and interatomic distances. The average Yb valence is found independent of temperature νav ∼ 2.42. Such a low Yb valence is hardly compatible with the occurrence of local magnetism on Yb inferred from a previous study. The pressure dependence of the Yb valence at 10 K does not reveal any first-order transition. The average Yb valence increases continuously under pressure but remains far from trivalency (νav ∼2.63) even under the highest external pressure used of 37 GPa.

Structures of Three Alkaline-Earth Metal Germanides Refined from Single-Crystal X-ray Diffraction Data

The calcium- and strontium- alumo-germanides SrxCa1–xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been synthesized and structurally characterized. Additionally, a binary calcium germanide CaGe has also been identified as a byproduct. All three crystal structures have been established from single-crystal X-ray diffraction methods and refined with high accuracy and precision. The binary CaGe crystallizes with a CrB-type structure in the orthorhombic space group Cmcm (no. 63; Z = 4; Pearson symbol oC8), where the germanium atoms are interconnected into infinite zigzag chains, formally [Ge]2−. The calcium atoms are arranged in monocapped trigonal prisms, centered by Ge atoms. SrxCa1−xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been confirmed to crystallize with a CaAl2Si2-type structure in the trigonal space group P3¯m1 (no. 164; Z = 1; Pearson symbol hP5), where the germanium and aluminum atoms form puckered double-layers, formally [Al2Ge2]2−. The calcium atoms are located between the layers and reside inside distorted octahedra of Ge atoms. All presented structures have a valence electron count satisfying the octet rules (e.g., Ca2+Ge2− and Ca2+[Al2Ge2]2−) and can be regarded as Zintl phases.

New Dy3+-activated KCa2Nb3O10 yellow-emitting phosphors for w-LEDs application: Preparation and optical properties

A novel single-phase KCa 2 Nb 3 O 10 :Dy 3+ yellow-emitting phosphor can be efficiently excited under 388 nm irradiation. • KCa 2 Nb 3 O 10 :Dy 3+ phosphors have been firstly synthesized using the molten-salt method. • The KCa 2 Nb 3 O 10 :Dy 3+ product shows excellent thermal stability with high temperature quenching temperature. • The KCa 2 Nb 3 O 10 :Dy 3+ product shows rich UV excitation band and yellow light emission. • The CIE color coordinates of prepared KCa 2 Nb 3 O 10 :Dy 3+ phosphors change slightly. A series of Dy 3+ doped KCa 2 Nb 3 O 10 niobate phosphors that generated yellow emission was prepared using the molten-salt method. The crystal structure, X-ray diffraction (XRD), optimal concentration, photoluminescence excitation/emission (PLE/PL), and luminescent stability of the prepared phosphors were exhaustively studied. The KCa 2 Nb 3 O 10 lattice has a perovskite-like structure, which possesses the Cmcm (No.63) space group. The KCa 2 Nb 3 O 10 :Dy 3+ phosphors can be efficiently excited by n -ultraviolet ( n -UV) excitation of 388 nm. Besides, KCa 2 Nb 3 O 10 :Dy 3+ phosphors can emit three dominant peaks centered at 486, 577, and 662 nm, which are ascribed to the 6 H J /2 ( J = 15/2, 13/2, and 11/2) transitions, respectively. The optimum doping concentrations of Dy 3+ ions in the KCa 2 Nb 3 O 10 host are determined to be 0.02 mol. The thermal-quenching temperature ( T 0.5 ) for the KCa 2 Nb 3 O 10 :0.20Dy 3+ sample is estimated to be above 500 K, and the calculated activation energy ( E a ) is 0.29 eV. Furthermore, the Commission International de I'Eclairage (CIE) color coordinates of prepared KCa 2 Nb 3 O 10 :Dy 3+ phosphors change slightly. KCa 2 Nb 3 O 10 :Dy 3+ phosphors possess good color purity, color stability, and low correlated color temperature (CCT). All results indicate that the KCa 2 Nb 3 O 10 :Dy 3+ phosphors are suitable for white light-emitting diodes (w-LEDs) applications.

An organic-inorganic hybrid cadmium chloride with face-sharing CdCl6 octahedral chains: Synthesis, crystal structure, optical and conduction mechanisms: [NH2(CH3)2]5Cd3Cl11

Organic-inorganic cadmium halides have recently emerged as promising alternatives to conventional optoelectronic materials thanks to their fascinating physical properties. The hybrid organic-inorganic compound Penta-dimethylammonium-Undecachlorotricadmate (II) [(CH3)2NH2]5Cd3Cl11, denoted DMAPCC, was synthesized at room temperature and its optical and electrical properties were studied. The structure shows the orthorhombic system with the Cmcm space group. The Raman spectroscopy, at room temperature, confirmed the presence of organic and inorganic sub-lattices. The UV–visible confirms the disorder of the structure and the semiconducting behavior of this compound. Furthermore, the electrical measurement confirms the thermal analysis result. Indeed, the variation of exponent s indicates the overlapping small polaron tunneling (NSPT) conduction model described the two phases of this material.Keys-words: hybrid materials, Optical properties, thermal properties, electrical properties and conduction mechanism.

A Challenge toward Novel Quaternary Sulfides SrLnCuS3 (Ln = La, Nd, Tm): Unraveling Synthetic Pathways, Structures and Properties.

We report on the novel heterometallic quaternary sulfides SrLnCuS3 (Ln = La, Nd, Tm), obtained as both single crystals and powdered samples. The structures of both the single crystal and powdered samples of SrLaCuS3 and SrNdCuS3 belong to the orthorhombic space group Pnma but are of different structural types, while both samples of SrTmCuS3 crystallize in the orthorhombic space group Cmcm with the structural type KZrCuS3. Three-dimensional crystal structures of SrLaCuS3 and SrNdCuS3 are formed from the (Sr/Ln)S7 capped trigonal prisms and CuS4 tetrahedra. In SrLaCuS3, alternating 2D layers are stacked, while the main backbone of the structure of SrNdCuS3 is a polymeric 3D framework [(Sr/Ln)S7]n, strengthened by 1D polymeric chains (CuS4)n with 1D channels, filled by the other Sr2+/Ln3+ cations, which, in turn, form 1D dimeric ribbons. A 3D crystal structure of SrTmCuS3 is constructed from the SrS6 trigonal prisms, TmS6 octahedra and CuS4 tetrahedra. The latter two polyhedra are packed together into 2D layers, which are separated by 1D chains (SrS6)n and 1D free channels. In both crystal structures of SrLaCuS3 obtained in this work, the crystallographic positions of strontium and lanthanum were partially mixed, while only in the structure of SrNdCuS3, solved from the powder X-ray diffraction data, were the crystallographic positions of strontium and neodymium partially mixed. Band gaps of SrLnCuS3 (Ln = La, Nd, Tm) were found to be 1.86, 1.94 and 2.57 eV, respectively. Both SrNdCuS3 and SrTmCuS3 were found to be paramagnetic at 20–300 K, with the experimental magnetic characteristics being in good agreement with the corresponding calculated parameters.

Relaxor ferroelectric behaviour observed in (Ca0.5Sr0.5Ba0.5Pb0.5)Nb2O7 perovskite layered structure ceramics

Relaxor ferroelectric behaviour was observed in perovskite layered structure (PLS) (Ca0.5Sr0.5Ba0.5Pb0.5)Nb2O7 (CSBPN) ceramics engineered using the high entropy approach. The CSBPN ceramics were sintered at 1350 °C and are single-phase with an orthorhombic structure (Cmcm space group) at room temperature. Their relaxor ferroelectric behaviour is characterized by a broad and frequency-dependent permittivity maximum and a current peak around zero electric field in the hysteresis loop. The presence of polar nanoregions is supported by piezoresponse force microscopy images. The value of the relative permittivity ɛ′ = 130 at 1 kHz and room temperature is much larger than that for conventional PLS ceramics Sr2Nb2O7 (ɛ′ = 42) and Ca2Nb2O7 (ɛ′ = 38). This can be attributed to the presence of polar nanoregions and the lattice distortion effect in high entropy materials. The appealing dielectric and relaxor behaviour of CSBPN ceramics confirms the efficacy of the high entropy approach to obtain improved properties.

Effect of structural symmetry on magnetic, electrical and electrocatalytic properties of isoelectronic oxides A2LaMn2O7 (A= Sr 2+, Ca2+)

The impact of structural symmetry on electrical charge transport, magnetism and electrocatalytic activity has been investigated in isoelectronic materials Ca2LaMn2O7 and Sr2LaMn2O7. These oxides form the so-called Ruddlesden-Popper structure, comprising bilayer stacks of MnO6 octahedra, where Ca/Sr/La occupy the spaces within and between the stacks. The change in ionic radius from Ca2+ (1.18 Å) to Sr2+ (1.31 Å) results in a change in structural symmetry in these systems. Ca2LaMn2O7 has an orthorhombic structure with Cmcm space group, whereas Sr2LaMn2O7 features a tetragonal, I4/mmm, structure. The higher symmetry results in a significant variation of electrical, magnetic and electrocatalytic properties. Sr2LaMn2O7 shows significantly greater charge transport in the entire temperature range of 25–800 °C, owing to a larger angle of Mn–O–Mn conduction pathway. In addition, the electrocatalytic properties of Sr2LaMn2O7 for hydrogen-evolution reaction (HER) and oxygen-evolution reaction (OER) are enhanced as compared to Ca2LaMn2O7. This is manifested in the improved overpotential for both HER and OER, as well as enhanced reaction kinetics. The improved OER/HER activity is also a function of structural features that produce greater electrical conductivity, which in turn affects the electrocatalytic properties.

ACuZrQ3 (A = Rb, Cs; Q = S, Se, Te): Direct Bandgap Semiconductors and Metals with Ultralow Thermal Conductivity

ACuZrQ3 (A = Rb, Cs; Q = S, Se, Te) were synthesized as black platelet crystals. RbCuZrS3, RbCuZrSe3, and CsCuZrS3 crystallize in the KCuZrSe3 structure type with space group Cmcm, and RbCuZrTe3 and CsCuZrTe3 crystallize in the lower symmetry space group Pnma. The tellurides exhibit a second-order Jahn–Teller distortion with off-centering of Zr in its octahedral environment. The magnitude of the distortion is larger in RbCuZrTe3 than in CsCuZrTe3. The structures of β-CsCuS4 and Rb2Cu5Te5 were also determined. CsCuZrS3 melts at 910 °C and exhibits partial decomposition upon heating at 275 °C, while CsCuZrTe3 melts incongruently. Our DFT calculations of RbCuZrQ3 (Q = S, Se) and CsCuZrS3 indicate direct gap semiconductors in agreement with experiments. ACuZrTe3 (A = Rb, Cs) were calculated to be metals which was confirmed for RbCuZrTe3 with variable temperature conductivity measurements and consistent with heat capacity measurements. Spectroscopic measurements found a bandgap and work function of 1.44(5) eV and 4.89(5) eV for RbCuZrS3 and 0.95(5) eV and 4.67(5) eV for RbCuZrSe3, respectively. RbCuZrTe3 did not exhibit an optical bandgap and has a work function of 4.64(5) eV. RbCuZrTe3 exhibits a low thermal conductivity under 0.5 W m–1 K–1 at room temperature.

Superconductivity in Crystallographically Disordered LaHg6.4

The influence of structural disorder on superconductivity is not yet fully understood. A concurrent examination of crystallographic and physical properties of LaHg6.4 reveals that this material enters a superconducting state below Tc = 2.4 K while showing crystallographic disorder in one dimension. Lanthanum mercuride, which crystallizes in a new structure type (space group Cmcm, a = 9.779(2) Å, b = 28.891(4) Å, c = 5.0012(8) Å, Z = 8), has remained out of reach for nearly 50 years. In this crystal structure, strong disorder is present in the channels that propagate along the [001] direction. By implementing a combination of cutting-edge synthesis and characterization techniques, we were able to circumvent the complexity associated with the low formation temperature and chemical reactivity of this substance and study the superconductivity of LaHg6.4 in detail.

Photoelectrocatalytic CO2 reduction using stable lead-free bimetallic CsAgBr2 halide perovskite nanocrystals

• Rietveld refinement confirming the orthorhombic phase of CsAgBr 2 perovskite nanocrystals with space group Cmcm. • Crystalline nature of the CsAgBr 2 nanocrystals exhibiting photocatalytic CO 2 reduction. • High structural stability displayed by CsAgBr 2 nanocrystals (no degradation up to 6 months) in ambient conditions. • Thermally stable without loss of structural configuration up to 200 °C. • Superior photocatalytic CO 2 reduction with a CO yield ∼14 μmol g −1 h −1 and 50% Faradic efficiency. We report on the fabrication and systematic characterization of highly stable lead-free CsAgBr 2 perovskite nanocrystals (PNC) processed at room temperature without the involvement of any organic ligand. X-ray diffraction (XRD) measurements and Rietveld analysis of the data reveal that the synthesized perovskites are in the orthorhombic phase with space group Cmcm . The optical properties of the CsAgBr 2 PNC are analyzed by UV–Vis absorbance and photoluminescence spectra. Morphological studies are performed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Additionally, the high degree of structural stability of the PNC was reaffirmed by time-dependent XRD profiles, and the thermal stability was studied by Thermogravimetric analysis (TGA). PNC exhibit excellent air stability for up to six months and thermal stability up to 200 °C. Furthermore, we demonstrate superior photoelectrocatalytic CO 2 reduction using CsAgBr 2 PNC with around ∼14 μmol g −1 h −1 of CO yield and 50% Faradic efficiency.

Crystal structures, bond characteristics, and dielectric properties of novel middle-εr Ln3NbO7 (Ln = Nd, Sm) microwave dielectric ceramics with opposite temperature coefficients

This study synthesized two novel middle-εr Ln3NbO7 (Ln = Nd, Sm; named NNO and SNO) microwave dielectric ceramics through the classic solid-state process. The results of XRD and Rietveld refinement show that NNO and SNO ceramics formed pure phases with the space group Cmcm (63) and C2221 (20), respectively. The properties of Ln-O and Nb–O bonds of NNO and SNO ceramics were calculated based on the P–V–L theory. The Nb–O bonds positively affect the crystal structure stability of the two ceramics. The optimum microwave dielectric properties were obtained (NNO: εr = 31.61, Q·f = 6,615 GHz (at 6.10 GHz), and τf = −455.70 ppm/°C; SNO: εr = 34.55, Q·f = 11,625 GHz (at 5.77 GHz) and τf = 72.59 ppm/°C) when the samples sintered at 1550 °C. Notably, SNO ceramic shows a low dielectric loss and medium dielectric constant, and the opposite τf of NNO and SNO ceramics provide the possibility to fabricate microwave dielectric devices with good temperature stability.

Development of Efficient Photocatalyst MIL-68(Ga)_NH2 Metal-Organic Framework for the Removal of Cr(VI) and Cr(VI)/RhB from Wastewater under Visible Light

Severe environmental pollution is caused by the massive discharge of complex industrial wastewater. The photocatalytic technology has been proved as an effective way to solve the problem, while an efficient photocatalyst is the most critical factor. Herein, a new photocatalyst MIL-68(Ga)_NH2 was obtained by hydrothermal synthesis and were characterized by PXRD, FTIR, 1H NMR, and TGA systematically. The result demonstrates that MIL-68(Ga)_NH2 crystallized in orthorhombic system and Cmcm space group with the unit cell parameters: a = 36.699 Å, b = 21.223 Å, c = 6.75 Å, V = 5257.6 Å3, which sheds light on the maintenance of the crystal structure of the prototype material after amino modification. The conversion of Cr(VI) and binary pollutant Cr(VI)/RhB in wastewater under visible light stimulation was characterized by the UV-vis DRS. Complementary experimental results indicate that MIL-68(Ga)_NH2 exhibits remarkable photocatalytic activity for Cr(VI) and the degradation rate reaches as high as 98.5% when pH = 2 and ethanol as hole-trapping agent under visible light irradiation with good reusability and stability. Owing to the synergistic effect between Cr(VI) and RhB in the binary pollutant system, MIL-68(Ga)_NH2 exhibits excellent catalytic activity for both the pollutants, the degradation efficiency of Cr(VI) and RhB was up to 95.7% and 94.6% under visible light irradiation for 120 min, respectively. The possible removal mechanism of Cr(VI)/RhB based on MIL-68(Ga)_NH2 was explored. In addition, Ga-based MOF was applied in the field of photocatalytic treatment of wastewater for the first time, which broadened the application of MOF materials in the field of photocatalysis.

Stabilizing superconductivity of ternary metal pentahydride hbox {CaCH}_{{5}} via electronic topological transitions under high pressure from first principles evolutionary algorithm

We explored the phase stability of ternary pentahydride hbox {CaCH}_{{5}} based on the first principles evolutionary algorithm. Here, we successfully search for a candidate structure up to 500 GPa. As a consequence, the possible stable structure of hbox {CaCH}_{{5}} is found be to a monoclinic structure with space group Pm at a pressure of 50 GPa. Moreover, the orthorhombic structure with a space group of Cmcm is found to be thermodynamically stable above 316 GPa. With this, the Kohn-Sham equation plays a crucial role in determining the structural stability and the electronic structure. Therefore, its structural stability is discussed in term of electronic band structure, Fermi surface topology, and dynamic stability. With these results, we propose that the superconducting transition temperature (hbox {T}_{{c}}) of Cmcm structure is estimated to be 50 K at 450 GPa. This could be implied that the proposed Cmcm structure may be emerging as a new class of superconductive ternary metal pentahydride. Our findings pave the way for further studies on an experimental observation that can be synthesized at high pressure.

Li5Sn, the Most Lithium-Rich Binary Stannide: A Combined Experimental and Computational Study.

From reaction of excess lithium with tin, we isolate well-crystallized Li5Sn and solve the crystal structure from single-crystal X-ray diffraction data. The orthorhombic structure (space group Cmcm) features the same coordination polyhedra around tin and lithium as previously predicted by electronic structure calculations for this composition, however differently arranged. An extensive ab initio analysis, including thermodynamic integration using Langevin dynamics in combination with a machine-learning potential (moment tensor potential), is conducted to understand the thermodynamic stability of this Cmcm Li5Sn structure observed in our experiments. Among the 108 Li5Sn structures systematically derived using the structure enumeration algorithm, including the experimental Cmcm structure and those obtained in previous ab initio studies, another new structure with the space group Immm is found to be energetically most stable at 0 K. This computationally discovered Immm structure is also found to be thermodynamically more stable than the Cmcm structure at finite temperatures, indicating that the Cmcm Li5Sn structure observed in our experiments is favored likely due to kinetic reasons rather than thermodynamics.

Magnetic ordering and magnetocalori effect of GdNiGa4, GdNi0.5Ga1.5 and GdNiGa

The polycrystalline YNiAl4-type GdNiGa4 (space group Cmcm, N 63, oC24), CeCu2-type GdNi0.5Ga1.5 (space group Imma, N 74, oI12) and TiNiSi-type GdNiGa (space group Pnma, N 62, oP12) are prepared by arc melting with following annealing. The magnetic ordering and magnetocaloric effects of these compounds have been investigated using magnetic measurements in fields up to 90 ​kOe GdNiGa4 shows field insensitive antiferromagnetic ordering below TN ​= ​12 ​K, GdNi0.5Ga1.5 demonstrate ferromagnetic ordering below TC ​= ​36 ​K and low-temperature field-sensitive ferro-antiferromagnetic ordering (Tm) in the range of 12–32 ​K, while GdNiGa exhibits ferromagnetic ordering below TC ​= ​28 ​K. The saturation magnetizations at 2 ​K indicate a collinear ferromagnetic ordering of Gd-sublattice in GdNi0.5Ga1.5 and GdNiGa. The transformation of crystal lattice from GdNi0.5Ga1.5 to GdNiGa with ordering of Ni-sublattice leads to a remarkable increasing of magnetic entropy change and magnetocaloric effect. The structural and magnetic features of ternary Gd-Ni-Ga compounds are discussed.

Oxide Ion Conductivity, Proton Conductivity, and Phase Transitions in Perovskite-Derived Ba3-x Sr x YGa2O7.5 0 ≤ x ≤ 3 Materials.

We report the synthesis, structural characterization, and oxide ion and proton conductivities of the perovskite-related Ba3–xSrxYGa2O7.5 family. Single-phase samples are prepared for 0 ≤ x ≤ 3 and show a complex structural evolution from P2/c to C2 space groups with an increase in x. For 1.0 ≲ x ≲ 2.4, average structures determined by X-ray and neutron powder diffraction show metrically orthorhombic unit cells, but HAADF-STEM imaging reveals this is caused by microstructural effects due to intergrowths of the Ba- and Sr-rich structure types. Variable-temperature powder diffraction studies suggest that 0 ≲ x ≲ 2.4 compositions undergo a phase transition upon being heated to space group Cmcm that involves disordering of the oxygen substructure. Thermal expansion coefficients are reported for the series. Complex impedance studies show that the Ba-rich samples are mixed proton and oxide ion conductors under moist atmospheres but are predominantly oxide ion conductors at high temperatures or under dry atmospheres. Sr-rich samples show significantly less water uptake and appear to be predominantly oxide ion conductors under the conditions studied.

Ferromagnetic ordering in UFe0.40Ge[formula omitted] studied by [formula omitted]Fe Mössbauer spectroscopy

A polycrystalline 57Fe-isotope-enriched sample of UFe0.40Ge2 was investigated by X-ray powder diffraction, magnetization and Mössbauer spectra measurements. The compound was confirmed to crystallize with the orthorhombic CeNiSi2-type structure (space group Cmcm) and with the lattice parameters a = 4.0759(2) Å, b = 15.8107(7) Å, and c = 4.0379(2) Å, being close to those reported previously for a very similar composition. Magnetic properties measurements showed that UFe0.40Ge2 orders ferromagnetically at TC = 37 K with the effective magnetic moment of 2.57(3) μB and the ordered magnetic moment at 70 kOe of about 0.64(1) μB, being fully consistent with the earlier report on physical properties of UFe0.39Ge2. 57Fe Mössbauer spectra measurements performed both in the field-cooled and zero-field-cooled regimes ruled out the formation of ferromagnetic cluster-glass or spin-glass state, and confirmed that the ferromagnetism in the studied system is purely long-range in nature. A small contribution of about 0.24–0.36 μB to the total magnetic moment from the iron atoms was observed.