The phase structure,thermodynamic properties,and dissolution behavior of Ca5Mg4V6O24

A Ca₅Mg₄V₆O₂₄ compound was synthesized through solid-state roasting routes under an air atmosphere, and its crystal structure and thermodynamic properties were determined using various methods. The cell parameters of Ca₅Mg₄V₆O₂₄ indicate that it crystallizes in cubic space group Ia3d with the unit cell parameters a = 12.442 ± 0.001 Å. X-ray photoelectron spectroscopy also confirmed that the vanadium element in the Ca₅Mg₄V₆O₂₄ sample is present in the +5 state. The melting of Ca₅Mg₄V₆O₂₄ was detected at 1442 K. The molar heat capacity (374 J mol K⁻¹) and entropy (688.2 J mol K⁻¹) of Ca₅Mg₄V₆O₂₄ at 298.15 K were determined using physical properties measurement system, and simultaneous thermal analyzer for the first time. The solubility of Ca₅Mg₄V₆O₂₄ in water at different temperatures was measured and its dissolution behavior in sulfuric acid and kinetics was experimentally established.     

Electrochemical Determination of Gibbs Energy of Formation of LaCrO3 Using a Composition‐Graded Bielectrolyte

Presented are new measurements of the standard Gibbs free energy of formation of rhombohedral LaCrO₃ from component oxides La₂O₃ and Cr₂O₃ in the temperature range from 875 to 1175 K, using a bielectrolyte solid‐state cell incorporating single crystal CaF₂ and composition‐graded solid electrolyte (LaF₃)_y·(CaF₂)_1?y (y = 0–0.32). The results can be represented analytically as (±2270)/J·mol^?1 = ?72329 + 4.932 (T/K). The measurements were undertaken to resolve serious discrepancies in the data reported in the literature. A critical analysis of previous electrochemical measurements indicates several deficiencies that have been rectified in this study. The enthalpy of formation obtained in this study is consistent with calorimetric data. The standard enthalpy of formation of orthorhombic LaCrO₃ from elements at 298.15 K computed from the results of this study is /kJ·mol^?1 = ?1536.2 (±7). The standard entropy of orthorhombic LaCrO₃ at 298.15 K is estimated as 99.0 (±4.5) J·(mol·K)^?1.     

Thermodynamic properties of sodium trititanate (Na2Ti3O7) at high temperature (298.15-1403 K)

Sodium-ion batteries (NaIBs) have attracted extraordinary attentions as a promising scalable energy storage alternative to current lithium-ion batteries (LIBs), owing to their natural abundance and low costs. Sodium trititanate (Na₂Ti₃O₇) is a promising material as the material of NaIBs with low potential and high theoretical capacitance. In order to better understand their service performance when utilized in rechargeable NaIBs, studies on thermodynamic properties of Na₂Ti₃O₇ are indispensable. However, an extensive literature review revealed that the heat capacity of Na₂Ti₃O₇ is established with divergences, especially for high-temperature region. Therefore, the 99.5% purity of Na₂Ti₃O₇ powder was first Synthesized through solid-state reaction with sodium carbonate (Na₂CO₃) and titanium dioxide (TiO₂) as raw materials. The as-prepared samples were used to measure the heat capacity from 573 to 1323 K which was carried out with multihigh temperature calorimeter (MHTC) 96 line. The temperature dependence of heat capacity was modeled as a function: Cp =255.51073 + 0.06059 T − 3.86912 × 106 T⁻² (J mol⁻¹ K⁻¹) (298.15 - 1403 K), and then used for computing changes in enthalpy, entropy, and Gibbs free energy. Heat capacity of Na₂Ti₃O₇ from 0 to 1403 K was given for future application of Na₂Ti₃O₇ in rechargeable batteries.     

Investigations on the polymorphism of K4CaSi6O15 at elevated temperatures

In the present study, single crystals and polycrystalline material of K₄CaSi₆O₁₅ were prepared from solid-state reactions between stoichiometric mixtures of the corresponding oxides/carbonates. Heat capacity (C_p) measurements above room temperature using a differential scanning calorimeter indicated that two thermal effects occurred at approximately T₁ = 462 K and T₂ = 667 K, indicating the presence of structural phase transitions. The standard third-law entropy of K₄CaSi₆O₁₅ was determined from low-temperature C_p’s measured by relaxation calorimetry using a Physical Properties Measurement System and amounts to S°(298K) = 524.3 ± 3.7 J·mol⁻¹·K⁻¹. For the 1^st transition, the enthalpy change ΔH^tr1 = 1.48 kJ·mol and the entropy change ΔS^tr1 = 3.25 J·mol⁻¹·K⁻¹, whereas ΔH^tr2 = 3.33 kJ·mol⁻¹ and ΔS^tr2 = 5.23 J·mol⁻¹·K⁻¹ were determined for the 2^nd transition. The compound was further characterized by in-situ single-crystal X-ray diffraction between ambient temperature and 1063 K. At 773 K, the high-temperature phase stable above T₂ has the following basic crystallographic data: monoclinic symmetry, space group P2₁/c, a = 6.9469(4) Å, b = 9.2340(5) Å, c = 12.2954(6) Å, β = 93.639(3)°, V = 787.13(7) ų, Z = 2. It belongs to the group of interrupted framework silicates and is based on tertiary (Q³-type) [SiO₄]-tetrahedra. Together with the octahedrally coordinated Ca-cations, a three-dimensional mixed polyhedral network structure is formed, in which the remaining K-ions provide charge balance by occupying voids within the net. The intermediate temperature modification stable between T₁ and T₂ shows a (3+2)-dimensional incommensurately modulated structure that is characterized by the following q-vectors: q₁ = (0.057, 0.172, 0.379), q₂ = (-0.057, 0.172, -0.379). The crystal structures of the high- and the previously studied ambient temperature polymorph (space group Pc) are topologically equivalent and show a group-subgroup relationship. The index of the low- in the high-symmetry group is six and involves both, losses in translation as well as point group symmetry. The distortion is based on shifts of the different atom species and tilts of the 4- and 6-fold coordination polyhedra. Actually, for some of the oxygen atoms, the displacements exceed 0.5 Å. A more detailed analysis of the distortions relating to both structures has been performed using mode analysis, which revealed that the primary distortion mode transforms according to the Λ₁ irreducible representation of P2₁/c. However, other modes with smaller distortion amplitudes are also involved.     

A new ternary phase in the system CaO–Al2O3–Cr2O3: Crystal structure and thermal expansion of CaAl2Cr2O7

Polycrystalline material of a novel phase in the system CaO–Al₂O₃–Cr₂O₃ has been obtained by solid-state reactions. Chemical analysis indicated the composition CaAl₂Cr₂O₇. Single-crystal growth of the new compound using borax as a mineralizer was successful. Diffraction experiments at ambient conditions on a crystal with composition CaAl_2.13Cr_1.87O₇ yielded the following basic crystallographic data: space group P 3, a = 7.7690(5) Å, c = 7.6463(5) Å, V = 399.68(6) ų, Z = 3. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 2.3% for 1440 independent observed reflections and 113 parameters. To the best of our knowledge, the structure of CaAl_2.13Cr_1.87O₇ or CaAl₂Cr₂O₇ represents a new structure type. It belongs to the group of double layer structures where individual double layers contain octahedrally and tetrahedrally coordinated cation positions. Linkage between neighboring sheet packages is provided by additional calcium cations. Furthermore, thermal expansion has been studied in the interval between 29 and 790°C using in situ high-temperature single-crystal diffraction. No indications for a structural phase transition were observed. From the evolution of the lattice parameters the thermal expansion tensor has been obtained. A pronounced anisotropy is evident. The response of structural building units to variable temperature has been discussed.     

Synthesis,structural feature and properties of rosiait structure compound BiGeSbO6

The layered oxide BiGeSbO₆ has been synthesized for the first time via solid state reaction. Rietveld refinement showed that BiGeSbO₆ belongs to PbSb₂O₆ structural type (P-31m space group) with unit cell parameters a = 5.1314(9), c = 4.9974(1) Å, α = 90°, γ = 120°, Z = 1. Using the EXAFS and XANES methods, it was shown that a structural feature of this compound is a strong disordering of the Bi–O octahedron caused by the stereochemical activity of the 6s² lone pair of Bi³⁺ electrons. A model according to which one oxygen vertex in the oxygen coordinated Bi³⁺ octahedron is absent, and the lone pair of electrons builds this polyhedron to the octahedron, was proposed. A particularity of the structure of BiGeSbO₆ is that the existing oxygen vacancy does not have a specific position. It was established that BiGeSbO₆ does not exhibit any polymorphic transition up until its incongruent melting point Т_m = 985°С. Isobaric heat capacity was measured and thermodynamic functions (entropy, enthalpy increment and Gibbs free energy) were calculated for BiGeSbO₆ in the 10–1200 K temperature range. We found that the band gap of BiGeSbO₆ is due to the allowed direct interband transition with the energy of 3.16 eV. It was shown that BiGeSbO₆ has a wide transmission region in the visible and near-IR ranges. BiGeSbO₆ is a self-activated phosphor, but its luminescence spectrum is atypical for Bi³⁺-containing oxides. The luminescent properties of Bi_1-xEu_xGeSbO₆ solid solutions (x = 0.3, 0.5) were also studied.     

K4CaSi6O15—Solving a 90-year-old riddle

Polycrystalline K₄CaSi₆O₁₅ was prepared from (a) solid-state reactions between stoichiometric mixtures of the corresponding oxides/carbonates and (b) combustion solution synthesis using K- and Ca-nitrates, tetraethyl orthosilicate (TEOS), and glycine (fuel component) as starting reagents. The compound was characterized by powder X-ray diffraction. Differential thermal analysis indicated that K₄CaSi₆O₁₅ melts congruently at about 956°C. On cooling down from the liquid state, a distinct glass-forming tendency was observed. Single crystals suitable for further structural investigations were obtained from sinter experiments just below the melting point. Basic crystallographic data are as follows: monoclinic symmetry, space group Pc, a = 6.9299(2) Å, b = 27.3496(9) Å, c = 12.2187(4) Å, β = 93.744(3)°, V = 2310.86(13) ų, Z = 3. The crystal structure of K₄CaSi₆O₁₅ belongs to the group of interrupted framework silicates with exclusively Q³-units. The tetrahedral network is the first inorganic representative of the so-called eth-type. Charge compensation in the structure is achieved by the incorporation of potassium and calcium cations, which are coordinated by five to nine oxygen ligands. Ninety years after its first mention the present contribution proves the existence of K₄CaSi₆O₁₅ as a stable phase in the ternary system K₂O–CaO–SiO₂.     

Thermodynamic Properties of LaCrO4, La2CrO6, and La2Cr3O12, and Subsolidus Phase Relations in the System Lanthanum–Chromium–Oxygen

In the system La–Cr–O, there are three ternary oxides (LaCrO₄, La₂Cr₃O₁₂, and La₂CrO₆) that contain Cr in higher valence states (V or VI). On heating, LaCrO₄ decomposes to LaCrO₃, La₂Cr₃O₁₂ to a mixture of LaCrO₄ and Cr₂O₃, and La₂CrO₆ to LaCrO₃ and La₂O₃ with loss of oxygen. The oxygen potentials corresponding to these decomposition reactions are determined as a function of temperature using solid‐state cells incorporating yttria‐stabilized zirconia as the electrolyte. Measurements are made from 840 K to the decomposition temperature of the ternary oxides in pure oxygen. The standard Gibbs energies of formation of the three ternary oxides are derived from the reversible electromotive force (EMF) of the three cells. The standard enthalpy of formation and standard entropy of the three ternary oxides at 298.15 K are estimated. Subsolidus phase relations in the system La–Cr–O are computed from thermodynamic data and displayed as isothermal sections at several temperature intervals. The decomposition temperatures in air are 880 (±3) K for La₂Cr₃O₁₂, 936 (±3) K for LaCrO₄, and 1056 (±4) K for La₂CrO₆.     

Structural,magnetic and dielectric properties of Cr substituted yttrium iron garnets

Chromium substituted polycrystalline Yttrium Iron Garnets (Y₃Fe_5–xCr_xO₁₂ with x = 0 to 0.5) were prepared in single‐phase form with lattice constant in the range of 12.3775 Å to 12.3560 Å. All samples exhibit ferrimagnetic transition with transition temperature (T_c) in the range of 547 K for x = 0 to 494 K for x = 0.5. The saturation magnetization value at room temperature is found to increase with Cr concentration that is, from 24.8 to 26.6 emu/g and this is attributed to the preferential occupation of Cr³⁺ ions at octahedral site of Fe³⁺ ions. The frequency dependence of impedance data shows the relaxation and thermal activation of charge carriers across grains and grain boundaries. The complex impedance spectra were modeled by considering equivalent circuits having contributions from the resistance and constant phase element due to grains and grain boundaries and capacitance across grain boundaries. The dielectric constant is found to increase from 20 to 52 as the Cr concentration is increased and it is attributed to hopping of charge carriers across Fe²⁺–Fe³⁺ centers. The Arrhenius plots of relaxation time of charge carriers and conductivity show an anomaly in the vicinity of ferrimagnetic transition temperature and it highlights the presence of magneto‐electric coupling.     

Synthesis and Crystal Structure of Na2Ba9Si20O50—An Intermediate Phase Along the Join Na2Si2O5‐BaSi2O5

Single crystals of Na₂Ba₉Si₂₀O₅₀ were obtained from solid state reactions performed along the join Na₂Si₂O₅‐BaSi₂O₅. The crystal structure has been determined from a data set collected at ambient temperatures and subsequently refined to a residual of R(|F|) = 0.0328 for 2211 independent reflections. The compound belongs to the group of phyllosilicates and adopts the monoclinic space group C2/m with the following lattice parameters: a = 39.111(3) Å, b = 7.6566(6) Å, c = 8.2055(6) Å, β = 97.319(6)°, V = 2437.2(3) Å³, Z = 2. Furthermore, weak one‐dimensional diffuse streaks running parallel to a* as well as a very small number of low intensity reflections at b*/3, indicating the presence of a superstructure, were observed. Basic buiding units are silicate layers parallel to (40‐1) which can be obtained from the condensation of single chains with a periodicity of four running along [010]. The sheets can be partitioned into two kinds of consecutive strips containing (i) a sequence of four‐ and eight‐membered rings and (ii) a four‐ring wide “zig‐zag shaped” unit consisting of exclusively six‐membered rings. The sodium and barium cations—distributed among six crystallographically independent positions—are sandwiched between subsequent layers and are linked to seven to nine nearest oxygen neighbors. The structure of Na₂Ba₉Si₂₀O₅₀ is closely related to that of K₂Ba₅Si₁₂O₃₀ and K₂Ba₇Si₁₆O₄₀, respectively. There are strong arguments that the previously claimed phase Na₄Ba₈Si₂₀O₅₀ is actually misinterpreted Na₂Ba₉Si₂₀O₅₀ and that the composition of the intermediate phase along the join Na₂Si₂O₅–BaSi₂O₅ is slightly different from that described in the literature.     

Structural characterization,energy transfer,and Judd–Ofelt analysis of pure and the Eu3+-doped Ca2LiMg2V3O12 phosphors

A novel vanadate host Ca₂LiMg₂V₃O₁₂ (CLMV) and the Eu³⁺-doped samples were synthesized via a solid-state reaction method. The phase formation and the morphological analysis were studied in detail. The Rietveld refinement result shows that the host belongs to cubic space group Ia-3d (230) with lattice parameter, a = 12.3948 Å, V = 1904.23 Å³, and Z = 8. The diffuse reflectance spectroscopy measurement estimated the bandgap of the host and the CLMV:0.05Eu³⁺ phosphors. The host exhibits a broad absorption band (peak at 345 nm) ranging from 240 to 380 nm, which is attributed to the charge transfer in the O²⁻–V⁵⁺ complex. Under near UV excitation (λ_exc = 345 nm), the host gives a broad emission band covering the visible region from 400 to 730 nm and the emission is in the bluish–green region of the CIE diagram. When the host is doped with the Eu³⁺ ions and excited at 345 nm, the emission spectrum depicts the superimposition of the characteristic emission bands (red emission) of the Eu³⁺ ions corresponding to the f–f transitions over the broad emission band of the host. The calculated color coordinates (9600 to 2280 K) demonstrated the color tuning ability of the phosphor as the dopant concentration is increased in the host. This is because the VO₄³⁻ group plays the sensitiser role and partially transfers energy with the Eu³⁺ ions. When the same set of phosphors were excited at the dominant characteristic excitation band (λ_exc = 394 nm) of the Eu³⁺, the characteristic emission bands of the Eu³⁺ in the orange–red region were observed. As the electric dipole transition of the Eu³⁺ was found to be dominant, the prepared phosphors possessed high color purity (CP). The energy transfer mechanism and the lifetime values were also presented. The temperature-dependent PL studies showed good thermal stability of the optimum sample. Various radiative transition properties were analyzed by the Judd–Ofelt theory. The photometric results reveal the color tuning ability and CP of the CLMV:xEu³⁺ phosphors.     

Thermodynamic Assessment of the Pr–O System

The Calphad method was used to perform a thermodynamic assessment of the Pr–O system. Compound energy formalism representations were developed for the fluorite α‐PrO_2–x and bixbyite σ‐Pr₃O_{5 ± x} solid solutions while the two‐sublattice liquid model was used to describe the binary melt. The series of phases between Pr₂O₃ and PrO₂ were taken to be stoichiometric. Equilibrium oxygen pressure, phase equilibria, and enthalpy data were used to optimize the adjustable parameters of the models for a self‐consistent representation of the thermodynamic behavior of the Pr–O system from 298 K to melting.     

Enhanced pyroelectric performance in potassium sodium niobate-based ceramics via multisymmetries coexistence design

Achieving excellent pyroelectric performance remains a challenge for lead-free piezoelectric ceramics. To meet the requirements of both an enhanced pyroelectric coefficient at room temperature and good thermal stability during the encapsulation of pyroelectric devices, (1–x)K_0.48Na_0.52NbO₃–xBi_0.5Ag_0.5ZrO₃–0.2%Fe₂O₃ (KNN–BAZ–Fe) lead-free ferroelectric ceramics with high Curie temperatures were prepared to obtain improved pyroelectric performance via the coexistence of multiple symmetries. The variation of BAZ content led to the formation of rhombohedral–orthorhombic–tetragonal phase boundary and promoted grain growth, resulting in the best pyroelectric coefficient (p = 5.09 × 10⁻⁴ C m⁻²°C⁻¹) and enhanced figures of merit (F_i = 0.2084 × 10⁻⁹ (m V⁻¹), F_v = 0.0142 m² C⁻¹, F_d = 0.0947 × 10⁻⁴ Pa^−1/2, and F_e = 17.66 J m⁻³ K⁻²) for infrared (IR) detection when x = 0.05. The room-temperature pyroelectric coefficient obtained in this study is approximately four times that of the pure KNN ceramic and is the maximum value reported for niobate-based piezoelectric ceramics. Moreover, compared with the poor thermal stability of barium titanate- and bismuth sodium titanate-based ceramics because of their ultralow Curie temperature or thermal depolarization temperature, the ceramics investigated here exhibit much better thermal stability because of their high Curie temperature (T_C > 300°C) and diffused phase-transition behavior, making them more adaptable for practical applications. These results suggest that KNN–xBAZ–Fe ceramics are attractive candidates for applications in the field of IR sensors.     

Excellent energy-storage property and thermal stability of PLZT-based antiferroelectric ceramics

(Pb, La)(Zr, Ti)O₃ antiferroelectric (AFE) materials are promising materials due to their energy-storage density higher than 10 J cm⁻³, but their low energy-storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb_0.9175La_0.055)(Zr_0.975Ti_0.025)O₃–xPb(Yb_1/2Nb_1/2)O₃ (PLZTYN100x) AFE ceramics were prepared via two-step sintering method and investigated thoroughly. With the doping of Yb³⁺ and Nb⁵⁺, the phase structure transforms from the orthorhombic phase (AFE_O) to the coexistence of the orthorhombic-and-tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (W_rec) is 6.8–8.2 J cm⁻³ at 30 kV mm⁻¹ in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of W_rec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.     

Ionothermal synthesis and crystal structure of a new layered nickel(II) diphosphate,DRM-1

A new layered ammonium nickel(II) diphosphate, (NH₄)₂[Ni₃(P₂O₇)₂(H₂O)₂], has been synthesized ionothermally in the ionic liquid 1-butyl-3-methyl imidazolium bromide and characterized by powder X-ray diffraction, elemental analysis, scaning electron microscopy, thermogravimetry etc. The results of the characterization show that the crystal adopts the monoclinic space group P2₁/a with the lattice constants a = 9.23529(2) Å, b = 7.98489(2) Å, c = 9.40772(2) Å, β = 100.2608(2)° and Z = 2. Its structure consists of chains of cis- and trans-edge-sharing [NiO₆]-octahedra linked via [P₂O₇] units to form layers of [Ni₃(P₂O₇)₂(H₂O)₂]^2? in the ab plane. Adjacent layers are separated in the c-direction by ammonium ions.     

Dielectric polarizability of SiO2 in niobiosilicate glasses

Understanding the mechanisms contributing to dielectric properties of glasses is critical for designing new compositions for microwave frequency applications. In this work, dielectric permittivity was measured using a cavity perturbation technique at 10 GHz for a series of niobiosilicate glasses with the compositions (100-2x)SiO₂- xNb₂O₅- xLi₂O where x = 32.5, 30, 25, and 15 mol%. Permittivity measurements and glass compositions were used to calculate the polarizability of each cation-anion unit in the glass network using the Clausius-Mossotti equation. The SiO₂ polarizability in niobiosilicates was calculated to be 6.16 ų, which is much higher than the SiO₂ polarizability in fused silica glass (5.25 ų), alkali modified silicates (5.37 ų), and aluminosilicates (5.89 ų). The increasing trend in SiO₂ polarizability is attributed to the disruption in the connectivity of the SiO₄ tetrahedral network as it accommodates different network formers. The high SiO₂ polarizability of 6.16 ų accurately predicts measured dielectric permittivity when Nb₂O₅ = 25, 30, and 32.5 mol%, but overpredicts measured permittivity when Nb₂O₅ ≤ 15 mol%, which is attributed to a decrease in SiO₂ polarizability as the percentage of corner sharing SiO₄ tetrahedra with NbO₆ octahedra goes down. This work demonstrates that SiO₂ polarizability depends on chemistry and connectivity of the glass, which has important implications in designing glass compositions for microwave frequency applications.     

Synthesis,crystal structure,characterization and magnetic property of a new organophosphonate-based polyoxovanadate

A novel organophosphonate-based polyoxovanadate, Cs_1·5Na_3.5[H{V₃(H₂O)O₃}{O₃PC- (OH)(CH₃)PO₃}₃]·15H₂O (1) has been synthesized and further investigated by single-crystal X-ray diffraction analysis, IR spectrum, UV–vis spectroscopy, X-ray powder diffraction, thermogravimetric analysis and X-ray photoelectron spectroscopy. Single-crystal X-ray analysis reveals that compound 1 crystallizes in the triclinic space group P-1 with a = 9.506(3) Å, b = 15.150(5) Å, c = 17.915(6) Å, V = 2437.9(14) ų and Z = 2. Compound 1 exhibits a ring-shaped cluster with three branches of the 1-hydroxyethane 1, 1-diphosphonic acid [HEDP = H₂O₃P(OH)C(CH₃)PO₃H₂] ligands. Furthermore, the magnetic property of compound 1 has also been studied.     

Effects of annealing temperature on structural and photoluminescence properties of Eu,Dy and Sm doped CaWO4 nanoparticles

Nanoparticles of xRe₂O₃ – (100-x)CaWO₄ (Re = Eu, Dy, Sm; x = 0, 1, 3, 5, 7 and 10 mol%) were synthesized by solid-state sintering at two annealing temperatures of 800 °C and 1150 °C and characterized by neutron diffraction, Raman and photoluminescence (PL) spectroscopy. The samples are composite materials and contain tetragonal CaWO₄ and cubic Re₂O₃ phases. The unit cell parameters, atomic position co-ordinates, crystallite size, mole-fraction of phases, bond-lengths, bond-angles and cation-oxygen co-ordination numbers were determined by Rietveld analysis of the neutron diffraction data. The short-range structure of CaWO₄ consists of snub disphenoid deltahedral CaO₈ and tetrahedral WO₄ units and the structure of cubic Re₂O₃ consists of two types of ReO₆ units. All the W–O bonds in WO₄ units are of equal lengths (1.77–1.79 Å) whereas two kinds of slightly different Ca–O bond-lengths (2.41–2.45 Å and 2.45–2.47 Å) exist in CaO₈ units. The neutron pair distribution function of the undoped CaWO₄ samples shows the first peak in the range of 1.71–1.74 Å due to W–O bonds and the second peak at 2.84 Å due to O–O and Ca–O pair correlations. Raman studies of Eu-doped samples show only W–O vibration modes, however, Sm and Dy-doped CaWO₄ show weak Raman peaks of Sm₂O₃ and Dy₂O₃, along with W–O bond vibrations. PL studies show highest orange-red emission at 1 mol% Sm₂O₃, green emission at 1 mol% Dy₂O₃ and red emission at 3 mol% Eu₂O₃. The light emission intensity in all the samples increases with the increase in annealing temperature from 800 °C to 1150 °C.     

Hydrothermal synthesis,crystal structure and magnetic properties of a novel nickel carboxylate–phosphonate with a layered structure

Hydrothermal reactions of N-(phosphonomethyl)proline (H₃L) with nickel sulfate hexahydrate resulted in a novel nickel carboxylate–phosphonate: |H₂O|[Ni₃(O₃PCH₂–NC₄H₇–CO₂)₂(H₂O)₄] (complex 1). Single-crystal X-ray diffraction analysis revealed that complex 1 crystallizes in the triclinic space group P-1 (No. 2), with lattice parameters of a = 10.0167(5) Å, b = 10.3882(5) Å, c = 11.9528(5) Å, α = 90.132(3)°, β = 107.246(3)°, γ = 111.158(3)°, V = 1099.39(9) Å³, and Z = 2. Complex 1 features a 2D layered structure. The structure contains alternating Ni-centered octahedra (Ni(1)O₆, Ni(2)O₅N and Ni(3)O₅N) and O₃PC tetrahedra linked to construct a layer with rhombohedral 12-MRs holes. The cyclopentylamine moieties of H₃L were grafted onto the layer through coordination of CPO₃, CO₂ and (CH₂)₂NCH₂ with central nickel atoms. These layers are stacked in an AA sequence, which results in a one-dimensional channel in the [001] direction. Water molecules are located in these channels. Magnetic studies showed that complex 1 exhibits predominantly paramagnetic behavior.     

A three-dimensional zincic molybdenum (V) phosphate with helical channel: Synthesis,structure, and electrochemical properties

A new reduced zincic molybdophosphate, (H₂bpp)₃[Zn₃Mo₁₂^VO₂₄(OH)₆(H₂O)₂(HPO₄)₆(PO₄)₂]·2H₂O 1 (bpp = 1,3-bis(4-pyridyl)propane) has been hydrothermally synthesized and characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction. Compound 1 crystallizes in the tetragonal space group I 41/a c d with a = 31.8033(4) Å, b = 31.8033(4) Å, c = 34.5593(8) Å, V = 34955.0(10) ų, and Z = 16 and exhibits a 4,6-connected 3-D framework with (3².8⁴)(3⁴.4².8³.9⁵.10) topology. The basic building blocks of [Zn(2)(Mo₆P₄)₂] are linked through [Zn(3)O₆] octahedra and [Zn(1)O₄] tetrahedra to construct 1-D chains along four different directions. Such 1-D chains are further connected by [Zn(1)O₄]²⁺ linkers to form a 3-D intricate framework with helical channels occupied by protonated bpp and water molecules. Additionally, the electrochemical property of the 1-CPE has been studied in detail.