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A new series of Ba2RE2Ge4O13 (RE = Pr, Nd, Gd, Dy) germanates and Ba2Gd2−xEuxGe4O13 (x = 0.1–0.8) solid solutions have been synthesized using the solid-state reaction technique and characterized by X-ray powder diffraction. All compounds crystallize in the monoclinic system, space group C2/c, Z = 4. The crystal lattice consists of RE2O12 dimers, zigzag C2-symmetric [Ge4O13]10− tetramers, and ten-coordinated Ba atoms located in voids between polyhedra. The density-functional theory (DFT) calculations performed on a rich set of Ba2RE2Ge4O13 compounds have confirmed the high thermodynamic stability of monoclinic modification. Under ultraviolet (UV) light excitation Ba2Gd2−xEuxGe4O13 phosphors exhibit an orange-red emission corresponding to the characteristic f–f transitions in Eu3+ ions. The highest intensity of lines at 580 nm (5D0 → 7F0), 582–602 nm (5D0 → 7F1), 602–640 nm (5D0 → 7F2), 648–660 nm (5D0 → 7F3), and 680–715 nm (5D0 → 7F4) is observed for the samples with x = 0.4–0.6. The possibility of their application has been assessed by studying their color characteristics, quantum efficiency, and thermal stability. The obtained data indicate that Ba2Gd2−xEuxGe4O13 solids can be considered as promising materials for UV-excited phosphor-converted light-emitting diodes (LEDs) if an aluminum nitride substrate (λex = 255 nm) is used as a semiconductor chip.

A new series of BaY2−xEuxGe3O10 (x = 0.1–0.8) trigermanates has been synthesized using the solid-state reaction method. A powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P21/m, Z = 2. The crystal lattice consists of distorted Y/EuO6 octahedra, trigermanate [Ge3O10]8− groups and Ba atoms located in eight-fold coordinated irregular sites. Under UV and 465 nm light excitation, the samples exhibit reddish-orange emission corresponding to the characteristic 5D0 → 7FJ transitions in Eu3+ ions. Concentration dependence study has shown that the powders with europium content x = 0.4–0.6 possess the highest luminescence intensity under 393 nm and 465 nm excitation. It has also been revealed that the predominant mechanism causing concentration quenching in the BaY2−xEuxGe3O10 series is due to multipolar interactions. The investigations on colour characteristics, quantum efficiency and thermal stability performance of BaY2−xEuxGe3O10 phosphors were carried out for the feasibility study of their practical application. The results indicate that BaY2−xEuxGe3O10 can be considered as a promising material for blue-excited phosphor-converted LEDs.

A new series of BaRE2Ge3O10 (RE = Y, Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) trigermanates has been prepared using a solid-state reaction. Powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P21/m, Z = 2. The crystal lattice consists of edge-sharing REO6 octahedra, bowed trigermanate [Ge3O10]8− groups, and Ba atoms located in eight-fold coordinated irregular sites. The geometry of [Ge3O10]8− anions persisting within different trigermanates has been examined with a special focus on the values of Ge–Ge–Ge angles and the types of conformation between the central and terminal GeO4 tetrahedra. The arrangement of [Ge3O10]8− anions in BaRE2Ge3O10 (RE = Y, Sc, Gd–Lu) crystal lattices is found to be unique. DFT calculations of different polymorphs for BaY2Ge3O10 and BaLa2Ge3O10 compounds have confirmed that our fabrication protocol yields all the products in their most thermodynamically stable forms. According to the results of vibrational spectroscopy studies, diffuse reflectance and photoluminescence measurements, the BaRE2Ge3O10 trigermanates are promising compounds for the preparation of efficient lanthanide ion activated phosphors.

A series of Sr3La2-xEux(Ge3O9)2 (x = 0.1–1.8) cyclogermanates has been prepared by the citrate method. The powder XRD study has shown that the compounds crystallize in the monoclinic space group C2/c, Z = 4. An increase in the dopant content causes a morphotropic phase transition: at x = 0.1–0.7 the samples are isostructural to Sr3La2(Ge3O9)2, while at x = 0.9–1.8 the germanates have a crystal structure of Sr3Eu2(Ge3O9)2. In all compounds, strontium and rare earth ions occupy three symmetry independent cation sites and form layers alternating along the [ 1 0 1 ¯ ] direction. The relationships between the crystal structure and the luminescence characteristics: the energy of the charge transfer transition, the values of 4f–4f/CTB and 5D0 → 7F2/5D0 → 7F1 intensity ratios have been revealed. CIE chromaticity coordinates for Sr3La1.4Eu0.6(Ge3O9)2 and Sr3La0.8Eu1.2(Ge3O9)2 phosphors under 393 nm excitation have been measured.

Solid solutions CaLa2-xEu x Ge3O10 (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa2Ge3O10, they crystallize in the monoclinic system, space group P21/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa2Ge3O10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

The formation conditions, crystal structure and luminescence properties of aluminum and gallium hydroxide diformates, Me(OH)(HCOO)2, have been established. Both compounds crystallize in a monoclinic lattice (space group C2, #5 and Z = 8) with parameters: a = 8.8629(2) A, b = 9.9890(2) A, c = 10.2411(1) A, β = 106.223(1)°, and V = 870.56(3) A3 (Al) and a = 8.8746(1) A, b = 10.3291(1) A, c = 10.27870(9) A, β = 105.7565(6)°, and V = 906.81(2) A3 (Ga). The emission spectra of Me(OH)(HCOO)2 under UV excitation with wavelength λ = 285 nm exhibit maxima in the range of 440–470 nm. The emission accompanied by light-blue luminescence is greatly enhanced when going from the aluminum to the gallium compound. The origin of intrinsic emission centers responsible for the luminescence properties of Me(OH)(HCOO)2 is suggested and the higher emission of the gallium hydroxide diformate is substantiated by means of density-functional theory calculations.

A promising series of phosphors based on Li7La3−xEuxHf2O12 (x = 0.05–0.20) has been prepared using a conventional solid state reaction. Rietveld refinement of room temperature powder X-ray diffraction patterns shows that the Li7La3−xEuxHf2O12 (x = 0.00–0.20) solid solution crystallizes in the tetragonal space group I41/acd, Z = 8. The trivalent europium ions occupy two crystallographically nonequivalent sites (8b) and (16e) with the D′2 and C2 symmetry, respectively. Raman spectroscopy corroborates the X-ray diffraction results and confirms the crystal structure features of tetragonal Li7La3Hf2O12 with the maximum phonon energy of 650 cm−1. The phosphors exhibit reddish orange emission under excitation at 282 nm. Calculation of the Ω2 and Ω4 Judd–Ofelt intensity parameters and quantum efficiencies from the recorded emission spectra allows a more extensive study of the luminescence properties of Eu3+-doped Li7La3Hf2O12. The maximum light emission is revealed at the activator content of x = 0.15 in Li7La3−xEuxHf2O12. CIE chromaticity coordinates of Li7La2.85Eu0.15Hf2O12 are x = 0.643 and y = 0.354.

The novel lithium tantalates doped with samarium ions were prepared using the solid state method. The single-phase Li5+xCaxLa3-xTa2O12:Sm3+ (x = 0; 1) compounds crystallize in the cubic space group Ia 3 ‾ d (Z = 8) and belong to the garnet family which is used for various optical applications. The diffuse reflectance, excitation and photoluminescence spectra measured at room and elevated temperatures are discussed in detail. The compounds demonstrate the well-known orange-red emission associated with the 4f-4f transitions in Sm3+ ions. The optimum samarium content in Li6CaLa2-xSmxTa2O12 solid solution is equal to 3 mol%, and the quenching mechanism is caused by the dipole-dipole interaction. Li6CaLa2-xSmxTa2O12 series provides higher luminescence intensity in comparison with Li5La3-xSmxTa2O12 samples. The CIE chromaticity coordinates are almost identical for all compounds and are equal to (0.61, 0.39). The Li6CaLa2Ta2O12:Sm3+ phosphors have good thermal stability of emission which allows one to consider these lithium calcium tantalate garnets as potential orange-red-emitting phosphors.

The phase formation of Sr3RЕ2(Ge3O9)2 (RE = Dy, Ho, Er, Tm, Yb, Lu) cyclogermanates was studied at 1000 and 1100 °C in air. It was shown that these compounds did not exist under these conditions, in contrast to cyclogermanates with large RE3+ ions, such as La, Pr, Nd, Sm, Eu and Gd. Using the thulium-based system SrO–Tm2O3–GeO2 as an example, it was established that compounds with Sr/RE atomic ratio other than 3/2 were formed instead of the expected Sr3RЕ2(Ge3O9)2. Single phase Sr4TmGe5.667O16.834 was prepared and characterized by X-ray powder diffraction. The quantum-chemical calculations confirmed the thermodynamic instability of strontium germanates Sr3RЕ2(Ge3O9)2 with RE3+ cations smaller than Gd3+. It is suggested that the prototypic structure of mixed strontium and Dy, Ho, Er, Tm, Yb and Lu rare earth germanates stems from the crystal structure of walstromite BaCa2Si3O9.

The crystal structure and luminescence properties of CaY2Ge3O10:Ln3+ (Ln = Eu, Tb) germanates synthesized via a conventional solid-state reaction and an ethylenediaminetetraacetic acid complexing process are studied. The CaY2 − xLnxGe3O10 (Ln = Eu, Tb; x = 0–1.0, 2.0; Δx = 0.1) solid solutions have a monoclinic structure (space group P21/c, Z = 4), in which dopant ions occupy three nonequivalent noncentrosymmetric sites with different Ca2+/Ln3+ ratios. The effect of the synthesis methods, dopant concentrations, and excitation wavelengths on the luminescence properties of the compounds obtained is determined.

DFT calculations with six LDA, GGA, and hybrid functionals have been performed using the CRYSTAL09 code to describe the crystal structure and vibrational spectra of Y2CaGe4O12 cyclotetragermanate, a new optical host. Two space groups P4/nbm and Cmme have been considered. The former corresponds to a mixed (0.5 Ca + 0.5 Y) distribution at the octahedral sites found from the results of Rietveld refinement of room temperature powder XRD pattern; the latter refers to the model of crystallographically nonequivalent calcium and yttrium atomic setting in distorted oxygen octahedrons. The most accurate geometry description has been obtained with the WC1LYP and PBE (n = 6) hybrid functionals, while the B3LYP calculation provides the best agreement between the recorded infrared and Raman spectra and their computed counterparts. Assignments of most of the observed bands to vibrational modes are given. The comparison between calculated and experimental frequencies shows a general good agreement for the spectra below 600 cm-1. The relationship between selected infrared bands and Raman lines, internal vibrations of the [Ge4O12] unit, and external modes is briefly discussed. © 2014 American Chemical Society.

The tetragermanate Ba2Eu2Ge4O13 was synthesized for the first time, and its structural and luminescent properties were examined. It crystallizes in a monoclinic system (space group C2/c, Z = 4) and its crystal structure incorporates a unique linear [Ge4O13]10− anion. The photoluminescence spectrum of the sample (λex = 280 nm) contains several intense peaks in the orange-red spectral range corresponding to the 4f–4f transitions in Eu3+ ions.

The novel red emitting phosphors based on CaY2−xEuxGe3O10 (x=0–2) have been prepared using both a conventional solid-state reaction and a synthesis route via EDTA-complexing process. Powder XRD study has revealed that CaY2−xEuxGe3O10 (x=0.1–0.8, 2.0) crystallizes in the monoclinic space group P21/c, Z=4. The trivalent europium ions occupy three different sites (4e) with the C1 symmetry. The phosphors exhibit a strong red emission under excitations at 250 nm and 393 nm. The light emission efficiency depends on the excitation wavelength, the activator content and the method of synthesis. Appropriate CIE chromaticity coordinates for CaY1.7Eu0.3Ge3O10 are x=0.54 and y=0.29.

The crystal structures of KCaVO4 and RbBaVO4, synthesized at high-pressure/high-temperature and by a conventional solid-state reaction, respectively, were determined using X-ray powder diffraction data. These compounds were found to have the β-K2SO4 structure type (space group Pnma, Z = 4) with parameters a = 7.2628(5) Å, b = 5.7258(4) Å, c = 9.6854(7) Å (KCaVO4), and a = 7.8887(1) Å, b = 5.9589(1) Å, c = 10.3958(2) Å (RbBaVO4). The unit cell volume of KCaVO4, 402.77(5) Å3, is significantly lower than for the low-temperature modification reported previously, 436.2 Å3. The difference can be explained by a pressure-induced phase transition to a more dense state resulting from the rotation of tetrahedra and the exchange of oxygen atoms from the first and second coordination spheres for potassium and calcium atoms.

A new series of promising luminescent materials, cyclosilicates Sr3R2(Si3O9)2, R=Y, Eu–Lu, has been synthesized via a solid-state reaction. X-ray and neutron powder diffraction studies show that these oxides crystallize in the monoclinic crystal system (S.G. C2/c, Z=4) and have a morphotropic phase transition between Er and Tm compounds followed by a step-like change of the unit cell constants. Isolated [Si3O9] rings located in layers are basic building units and stack with Sr/R layers along the [1 0 1 ¯ ] direction. The rare earth atoms are distributed among three independent Sr/R sites coordinated by 8, 7 and 6 oxygen atoms, and the Sr-R populations change from mixed to 0.5/0.5 over site (1) and full occupation of sites (2) and (3) by Sr and R, respectively, at the transition. Changes of the conformation and mutual arrangement of [Si3O9] rings, as well as exchange of oxygen atoms from the first and the second coordination sphere of two Sr/R sites also feature the phase transition. Luminescence in Sr3Y2(Si3O9)2:Eu3+ under ultraviolet (UV) excitation has been discussed.

A promising series of phosphors based on Li7La3−xEuxHf2O12 (x = 0.05–0.20) has been prepared using a conventional solid state reaction. Rietveld refinement of room temperature powder X-ray diffraction patterns shows that the Li7La3−xEuxHf2O12 (x = 0.00–0.20) solid solution crystallizes in the tetragonal space group I41/acd, Z = 8. The trivalent europium ions occupy two crystallographically nonequivalent sites (8b) and (16e) with the D′2 and C2 symmetry, respectively. Raman spectroscopy corroborates the X-ray diffraction results and confirms the crystal structure features of tetragonal Li7La3Hf2O12 with the maximum phonon energy of 650 cm−1. The phosphors exhibit reddish orange emission under excitation at 282 nm. Calculation of the Ω2 and Ω4 Judd–Ofelt intensity parameters and quantum efficiencies from the recorded emission spectra allows a more extensive study of the luminescence properties of Eu3+-doped Li7La3Hf2O12. The maximum light emission is revealed at the activator content of x = 0.15 in Li7La3−xEuxHf2O12. CIE chromaticity coordinates of Li7La2.85Eu0.15Hf2O12 are x = 0.643 and y = 0.354.

New germanate–vanadates with the general formula BiCa 4− x La x (VO 4 ) 3− x (GeO 4 ) x O, x =1−3, have been synthesized by the nitrate–citrate method and characterized. Structural refinement based on X-ray powder diffraction data showed that these compounds are isostructural with BiCa 4 (VO 4 ) 3 O (space group P6 3 /m (N 176), Z =2, а =9.8327–9.8755(3), and с =7.1203–7.2133(2) ). They may be viewed as continuous series of solid solutions where Ca 2+ and V 5+ cations in the crystal lattice of vanadate BiCa 4 (VO 4 ) 3 O are replaced by La 3+ and Ge 4+ cations. In the process of substitution, the La 3+ cations occupy mainly the 4f lattice sites of the germanate–vanadate oxyapatites, but the filling of the 4f and 6h lattice sites in the germanate BiCaLa 3 (GeO 4 ) 3 is equivalent. IR and Raman spectra were studied. The Raman spectra clearly show a two-mode behavior: the lines of GeO 4 and VO 4 are separated from each other, and the (V/Ge)O 4 tetrahedra exhibit a quasi-independent behavior.

The vanadium(V) complexes K[VO2(SeO4)(H2O)] and K[VO2(SeO4)(H2O)2] · H2O were synthesized using original procedures; their physicochemical properties were studied, and the crystal structure was determined on the basis of X-ray diffraction and neutron diffraction data. The structure of K[VO2(SeO4)(H2O)2] · H2O is composed of VO6 octahedra connected to form infinite chains by bridging SeO4 tetrahedra. Each VO6 tetrahedron has short terminal V-O bonds forming the bent dioxovanadium group VO2+ The unit cell parameters of K[VO2(SeO4)(H2O)2] · H2O are a = 6.4045(1) A, b = 9.9721(2) A, c = 6.6104(1) A, β = 107.183(1)°, V = 403.34 A3, Z = 2, monoclinic system, space group P21. The complex K[VO2(SeO4)(H2O)] forms a two-dimensional layered structure composed of highly distorted VO6 octahedra having two short terminal V-O bonds and SeO4 groups coordinated simultaneously by three vanadium atoms. This compound crystallizes in the monoclinic system (space group P21/c): a = 7.3783(1) A, b = 10.5550(2) A, c = 10.3460(2) A, β = 131.625(1)°, V = 602.894(5) A3, Z= 4. The vibrational spectra of the studied compounds are fully consistent with their structural features.

Synthesis was performed and physicochemical properties were studied for the M4V2O3(SO4)4 complexes, where M = K, Rb, or Cs. Their crystal structures were determined using the set of data from X-ray diffraction and neutron diffraction studies. All compounds crystallize in a triclinic lattice (space group \( P\bar 1 \) , Z = 2) with the parameters: a = 7.7688(2), 7.8487(1), 8.1234(1) A; b = 10.4918(3), 10.8750(2), 11.1065(1) A; c = 11.9783(4), 12.1336(2), and 11.8039(1) A; α = 76.600(2)°, 77.910(1)°, 79.589(1)°; β = 75.133(2)°, 75.718(1)°, 87.939(1)°; γ = 71.285(2)°, 72.189(1)°, 75.567(1)°; V = 881.78(5), 945.42(3), 1014.34(2) A3 for K, Rb, Cs, respectively. The structure of M4V2O3(SO4)4 was found to be formed by discrete complex anions V2O3(SO4)44− incorporating two oxygen-bridged vanadium atoms in a distorted octahedral oxygen environment. The sulfate groups are coordinated by the vanadium atoms in the chelating mode with a large scatter of S-O interatomic distances and OSO angles. Every VO6 octahedron has a short terminal vanadium-oxygen bond with a length of about 1.6A. The V2O3(SO4)44− complex anions in potassium and rubidium compounds differ from that in Cs4V2O3(SO4)4 in the type of symmetry and mutual spatial orientation. The vibrational spectra were presented and interpreted in line with the structural analysis data.

By the hydration of MVO(SeO(4))(2) with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition M[VO(2)(SeO(4))(H(2)O)(2)]center dot ...

Potassium oxosulfatovanadate(V) K3VO2(SO4)2 has been obtained by solid-phase synthesis from K2SO4, K2S2O7, and V2O5 (2: 1: 1), and its formation conditions, crystal structure, and physiochemical properties have been studied. The conversions of K3VO2(SO4)2 in contact with potassium vanadates and other potassium oxosulfatovanadates(V) are considered in terms of phase relations in the K2O-V2O5-SO3 system, which models the active component of vanadium catalysts for sulfur dioxide oxidation into sulfur trioxide. The X-ray diffraction pattern of K3VO2(SO4)2 is indexed in the monoclinic system (space group P21) with unit cell parameters of a = 10.0408(1) A, b = 7.2312(1) A, c = 7.3821(1) A, β = 104.457(1)°, Z = 2, and V = 519.02 A3. The crystal structure of K3VO2(SO4)2 is built from [VO2(SO4)2]3− complex anions, in which the vanadium atom is in an octahedral oxygen environment formed by two terminal oxygen atoms (V-O(6) = 1.605(7) A, V-O(10) = 1.619(7) A and four oxygen atoms of the two chelating sulfate anions. The vibrational spectra of K3VO2(SO4)2 are analyzed using these structural data.

Vanadium(V) complexes of general composition M3VO2(SO4)2 (M = Rb, Cs) were synthesized by a solid-state route. The individuality of the synthesized compounds was proved by X-ray and neutron diffraction, vibrational spectroscopy, and microscopic analysis. The X-ray diffraction patterns of M3VO2(SO4)2 were indexed to fit the monoclinic system (space group P2/c, Z = 4) with the following unit cell parameters: a = 11.6487(2) A, b = 8.4469(2) A, c = 12.1110(2) A, β = 109.483(1)°, V = 1123.43 A3 (Rb); a = 12.0546(3) A b = 8.7706(2) A, c = 12.6496(3) A, β = 109.843(2)°, V = 1257.99 A3 (Cs). In the crystal structure of M3VO2(SO4)2, [VO2(SO4)2]3− complex anions can be discerned in which the vanadium atom is surrounded by five oxygen atoms: two oxygen atoms form short terminal V–O bonds, and three oxygen atoms are from the two sulfato groups, one of which acts as a monodentate ligand and the other acts as a bidentate chelating ligand.

The crystal structure of the promising optical materials Ln{sub 2}M{sup 2+}Ge{sub 4}O{sub 12}, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y{sub 2-x}Er{sub x}CaGe{sub 4}O{sub 12} (x=0-2), Y{sub 2-2x}Ce{sub x}Ca{sub 1+x}Ge{sub 4}O{sub 12} (x=0-1), Y{sub 2}Ca{sub 1-x}Mn{sub x}Ge{sub 4}O{sub 12} (x=0-1) and Y{sub 2-x}Pr{sub x}MnGe{sub 4}O{sub 12} (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu{sub 2}MnGe{sub 4}O{sub 12} has been found. - Graphical abstract: Crystal structure of Ln{sub 2}MGe{sub 4}O{sub 12}, where Ln=rare-earth element or Y; M=Ca, Mn, Zn.

Compounds described as V2O3(XO4)2, where X = S or Se, were prepared from vanadium(V) oxide mixtures with concentrated sulfuric and selenic acids. The physicochemical properties of the products were studied; for V2O3(SeO4)2, the crystal structure was determined by powder X-ray diffraction and neutron diffraction, and its key differences from the structure of V2O3(SO4)2 were identified. V2O3(SeO4)2 crystallizes in the monoclinic system with the unit cell parameters a = 15.3831(2)A, b = 5.54096(5)A, c = 9.71644(7)A, β = 111.886(1)°, V = 768.51A3, space group C2/c (no. 15).

A crystal structure investigation of the low temperature Li2SnO3 modification has been carried out. X-ray, neutron powder and electron diffraction data showed that this compound crystallizes in a monoclinic unit cell with parameters: a = 5.3033(2)A, b = 9.1738(3)A, c = 10.0195(2)A, β ~ 100.042(2)o and has stacking disorder along the c-axis. Simulation of diffraction patterns with different stacking faults mainly reveal the presence of rotational stacking faults with a probability of about 40% . Introduction Lithium salts Li2MO3 (M = Sn, Ti, Zr, Mo, Pd, etc.) are candidate materials for Li ion conductors and solid breeders in a fusion reactor [1-3]. Li2SnO3 can also be used as a precursor for the synthesis of XSnO3 (X = Zn, Co, Ni) [4]. It has also been shown that, depending on the sintering conditions, the reactivity of Li2SnO3 is different [5]. As we will demonstrate, the reason for this could lie in the complex structural features of the compound. According to the literature, Li2SnO3 can be synthesized in two modifications. Lowtemperature (LT) Li2SnO3 is formed at temperatures below 800 oC and crystallizes in S.G. C2/m [6, 7]. High-temperature (HT) Li2SnO3 is formed at 1000 oC and also has a monoclinic unit cell (S.G. C2/c) with lattice parameters: a = 5.2889(2)A, b = 9.1872(3)A, c = 10.0260(2)A, β = 100.348(2)o [8]. Both modifications have a NaCl-related structure in which the oxygen atoms form a distorted cubic closed-packed network with octahedral cavities occupied by Li and Sn cations. Ordering of the metals along the [111] direction of the cubic body diagonal results in the appearance of two types of layers: one consists only lithium atoms (Li3) and another – lithium and tin atoms (LiSn2O6) (figure 1). The main difference between the HT and LT modifications lies in a different stacking of the LiSn2O6 layers. In spite of a lot of data from the literature the question about the exact crystal structure of the LT modification of Li2SnO3 is not clear yet. It was proposed in [6] and [7] that LT-Li2SnO3 376 European Powder Diffraction Conference, EPDIC 11 could just be a defect modification of the HT phase, and that the phase transition would correspond to a “healing” of the defects in the disordered structure. Figure 1. Crystal structure of HT-Li2SnO3. During our investigation of the interaction processes between lithium salts Li2MO3 (M = Zr, Sn, Ti) with evaporated water in an air environment and acid water solutions it has been shown that an extent of the exchange of Li ions for hydrogen, realized through the formation of Li2-xHxSnO3, depends on the sintering condition of the Li2MO3 precursors. For Li2SnO3 annealed at 700 oC the extent of the exchange of Li ions for hydrogen (x) is about 1.8, whereas for precursors annealed at 900-1100 oC the exchange x is ≤ 0.3 [5]. In order to clear out the origin of this difference in Li exchange, a structural investigation of Li2SnO3 has been carried out.

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln2Ga(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.

In the Mg4−xNixNb2O9 (0⩽x⩽4) system two ranges of solid solution have been found. One of the solid solutions has a corundum-related structure type (space group P 3 ¯ c 1 ); the second one adopts the II-Ni4Nb2O9 structure type (space group Pbcn). The unit cell constants and atomic positions have been determined and refined using neutron powder diffraction data. Electron diffraction and high-resolution transmission electron microscopy (HRTEM) from MgNi3Nb2O9 crystals identify the presence of planar defects and the intergrowth of several (structurally related) phases. The magnetic susceptibility of Mg3NiNb2O9, measured in the temperature range T=2–300 K, shows no indications of magnetic ordering at low temperatures, while for MgNi3Nb2O9 there is a magnetic ordering at temperatures below 45.5 K.

The crystal structure of dioxovanadium(V) sulfate trihydrates A[VO2(SO4)(H2O)2] · H2O, where A is K, Rb, Tl, or NH4, has been determined based on a combination of neutron and X-ray diffraction data. The compounds are isostructural and have a monoclinic lattice (space group P21, Z = 2) with unit cell parameters a = 6.24535(8), 6.26016(7), 6.25817(5), and 6.2500(1) A; b = 9.8417(1), 9.99736(8), 9.96217(9), and 9.9742(1) A; c = 6.52113(8), 6.69303(5), 6.70379(6), and 6.70334(9) A; β = 106.99(1)°, 107.83(1)°, and 107.83(1)°, 107.99(1)°, respectively. The SO4 tetrahedra and VO4(H2O)2 octahedra share an oxygen vertex to form infinite isolated chains. Atoms A have CN = 10. IR and Raman spectroscopy data are reported.

The crystal structure of alkali-metal dioxovanadium(V) sulfates AVO2SO4, where A is K or Rb, has been determined based on a combination of neutron and X-ray diffraction data. The compounds are isostructural and have an orthorhombic lattice (space group P212121, Z = 4) with unit cell parameters a = 11.1004(2) and 10.8193(1) A; b = 8.2626(2) and 8.9042(1) A; c = 5.4772(1) and 5.5722(1) A, respectively. The structures are of the chain type. Zigzag chains are formed by vertex-sharing VO6 octahedra. Sulfate groups SO4 link neighboring chains and form a spatial framework with cavities accommodating alkali-metal atoms with CN = 9 (K) and 8 (Rb). IR and Raman spectroscopy data are reported.

Complex oxides A 3 M 2 O 8 (A = Sr, Ba; M = P, As, V) with the palmierite structure (space group R -3 m (no. 166), Z = 3) [1‐6] are considered as promising ceramics, ionic conductors, and membrane materials. In the structures of these compounds, the A cations occupy 3 a and 6 c positions with coordination numbers (CN) of 6 and 10, respectively. The M cations occupy 6 c positions (CN = 4) and the O atoms are in 6 c and 18 h positions. The A 3 M 2 O 8 oxides are quite stable with respect to heterovalent replacement in the cationic (A, M) and anionic sublattices; for example, Ba 3 (W,Nb) 2 O 8 , Ba 3 Mo 2 O 6 N 2 , and Ba 3 W 2 O 6 N 2 were obtained [7, 8]. The double orthovanadates A 2 Ln 2/3 (VO 4 ) 2 with the palmierite structure were found in the A 3 (VO 4 ) 2 –LnVO 4 binary systems, where A = Ca, Sr, Ba; Ln = La, Nd [9, 10]. In this group of compounds, 6 c positions are statistically occupied by two sorts of cations, 0.3333 Ln 3+ and 0.5 A, while 3 a positions contain only one sort of cation (A). These compounds can be considered as the limiting compositions of solid solutions formed upon replacement of A atoms in the orthovanadates A 3 (VO 4 ) 2 , where A = Ca, Sr, Ba. Thus, if the valences are balanced, one can expect the formation of stable compounds upon any heterovalent substitution in the sublattices, which may be either complete or defective. However, no data on the A 3 M 2 O 8 oxides with heterovalent substitutions in the 3 a position have been reported. In this work, we report the results of synthesis and study of the structural and electronic properties of a new orthovanadate Sr 2 Bi 2/3 (VO 4 ) 2 in which Sr → Ba heterovalent substitution in the 3 a position is implemented for the first time. The compound was prepared by solid-phase synthesis from special purity grade bismuth and vanadium(V) oxides and strontium carbonate. The reactants were mixed and subjected to stepwise annealing in the temperature range 550–1100°e with a temperature rise by 100°e every 12‐15 h. The samples were pressed into

The crystal structure of the low-temperature form of K3PO4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma, Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO4] tetrahedra, with the potassium ions in between.

The new compounds CeNb7O12 and PrNb7O12, isostructural with LaNb7O12, have been synthesized and characterized by x-ray diffraction. The structures of the LnNb7O12 (Ln = La, Ce, Pr) compounds have space group P21/c (Z = 4), with lattice parameters a = 10.764(2), 10.743(2), 10.738(4) A; b = 9.192(2), 9.146(2), 9.137(3) A; c = 10.313(2), 10.304(2), 10.303(3) A; and β = 104.25(2)°, 104.31(2)°, and 104.21(3)°, respectively. The reduction in the lattice parameters of LnNb7O12 in going from La to Pr correlates with the ionic radii of Ln: r(La3+) > r(Ce3+) > r(Pr3+). In the Nd(Sm)-Nb-O systems, phases of stoichiometry LnNb7O12 have not been obtained.

The compound Na2ZnV2O7 with an åkermanite-type structure has been synthesized. It has a tetragonal unit cell, a=8.2711(4), c=5.1132(2) Å, and crystallizes with P-421m symmetry, Z=2. Its crystal structure has been refined from a combination of X-ray and neutron powder diffraction data. The structure contains layers of corner-sharing VO4 and ZnO4 tetrahedra, the former in pairs forming pyrovanadate V2O7 units. The sodium atoms are positioned between the layers, with a distorted antiprismatic coordination of oxygen atoms.

A new high-pressure, high-temperature phase, Zn4Nb2O9, has been prepared at T=1700 °C, using a pressure of P=9 GPa. An XRD study based on the Rietveld technique showed the structure to be corundum related ( P 3 c1 , Z=2) with the unit-cell parameters a=5.1864(1) A, c=14.1445(2) A. The structure consists of close-packed oxygen atoms, with 2/3 of the octahedral interstices occupied by zinc and niobium atoms. The space group was confirmed by micro diffraction and selected-area electron diffraction studies.

Phase formation at high pressures and temperatures were studied in the MnO–Nb(Ta)2O5 system. New rhombohedral modifications of Mn4Nb2O9 and Mn4Ta2O9, two new modifications of MnTa2O6, and two modifications of Mn2Ta2O7 were obtained. They were structurally identified.

A new high-pressure, high-temperature modification of Mn 4 Nb 2 O 9 , has been prepared at T =1700 °C, P =9 GPa. The XRD study based on Rietveld technique suggests the structure to be a rhombohedral (R3c) modification of Mn 4 Nb 2 O 9 , (LiNbO 3 type structure) with the chemical formula Mn(Mn 1/3 Nb 2/3 )O 3 and unit cell parameters a =5.34139(2), c =14.15807(7) A. However, electron diffraction (ED) and high resolution electron microscopy (HREM) images of crystallites found in an XRD single phase sample revealed frequent disorder, but also the existence of a new monoclinic modification of Mn 4 Nb 2 O 9 often intergrown with the corundum related P 3 c1-Mn 4 Nb 2 O 9 modification stable at ambient pressure and temperature. This new monoclinic modification has the unit cell parameters: a =9.93, b =5.34, c =13.20 A, β =92.9° and space group C2/c or Cc. It is closely related to the corundum lattice since its c ∗ axis is parallel to 〈2 0 2〉 ∗ R 3 c in the rhombohedral sublattice.

Synthesis conditions, crystal structures, and magnetic properties of quasi-one-dimensional complex oxides Ca3CuMnO6 (space group P-1, z=4, triclinic cell) and Ca3Co1+xMn1−xO6 with x=0, 0.25, 1.0 (structural type K4CdCl6, space group R-3c, z=6) are presented. The crystal structures of Ca3CoMnO6 and Ca3CuMnO6 were refined using neutron and combined X-ray and neutron diffraction analysis, respectively. The interatomic distances in oxygen polyhedra were found. In contrast to ferromagnetic Ca3Co2O6 (Tc=24 K), manganese-containing phases Ca3Co1+xMn1−xO6 are characterized by antiferromagnetic interactions with Neel temperatures 18 K (x=0.25) and 13 K (x=0). For Ca3CuMnO6TN was established to be 6 K.

The crystal structure of Pb 2 Fe(CN) 6 and Sn 2 Fe(CN) 6 has been first determined and refined using the Rietveld method with combined CuKα 1 X-ray and constant-wavelength neutron powder diffraction data in space group P -3 (147, Z =1). The unit cell constants are a =7.1346(1) and 7.1805(1) A, c =5.4531(2) and 5.3639(1) A, respectively. The compounds are layered, groups of three nearest [Fe(CN) 6 ] 4− -complexes are joined to layers by means of Pb or Sn atoms. The same Pb or Sn atoms (c.n.=3+3) joint three nearest complexes from the next layer. The jointing goes through ‘nitrogenlead(tin)nitrogen’ bonds.

This paper presents a cluster–DV study of the electronic structure of a large fragment of the crystal lattice of a new compound Pb2Fe(CN)6 having a trigonal structure. The electronic energy spectrum and electron density distribution between Fe–C, C–N, and Pb–N are discussed.

The phase compositions of theLaVO4-SrMoO4(1) and Sr2GeO4-SrMoO4 (2) binary systems, which bound the Sr2GeO4-LaVO4-SrMoO4 (3) ternary system, and the LaSr2(VO4)(GeO4)-Sr2GeO4+SrMoO4 section (4) of system 3 are studied at subsolidus temperatures. Systems 1 and 2 consist of a mixture of the initial compounds, and the La1 − xSr2 + x(GeO4)(V1 − xMoxO4) (where 0 ≤ x ≤ 0.4) region of substitutional solid solutions with a palmierite structure is formed in system 3. The unit cell parameters of the solid solutions are determined. The distribution of the lanthanum and strontium cations over two positions of the cationic sublattice is described.

The results of structural refinements and magnetic properties of one-dimensional oxide Ca 3 NiMnO 6 are presented. The structure of Ca 3 NiMnO 6 was solved by Rietveld analysis of powder neutron date in space group R -3 c with a =9.1227(9) A, c =10.5811(17) A, z=6 (type of K 4 CdCl 6 ). Infinite chains of MnO 6 octahedra and (Ni,Mn)O 6 trigonal prisms sharing faces run parallel to the c axis. The chains are separated by Ca 2+ cations, which are located in a distorted square antiprismatic environment. Magnetic susceptibility obeys the Curie-Weiss law at 300–600 K with μ eff value 5.00 μ B consistent with the valence cationic combination Ni 2+ -Mn 4+ . Magnetic measurements display the antiferromagnetic ordering in Ca 3 NiMnO 6 at 16 K.

Sr4−xNb17O26 (x=0.0, 0.3) and Eu4−xNb17O26 (x = 0.3) were synthesised from SrCO3/Eu2O3 and Nb2O5 in a vacuum furnace at temperatures up to 1600°C (1500°C for Eu) using acetylene soot or Nb as reducing agents. The synthetic studies show that these phases are only formed via an intermediate disordered ‘phase’ (or phasoid). Sr4−xNb17O26 and Eu4−xNb17O26 are isostructural with Ba4Nb17O26 and crystallise in space group P 4/m (83) with the unit cell parameters for x=0.3: a=12.023(l) A, c=4.1411(4) A and a=12.015(2) A c=4.1351l) A, Z = 1, respectively. The crystal structure can be described as an intergrowth between ANbO3 and NbO. Characteristic building blocks are quadruple chains of corner-sharing Nb6-octahedra. ?The structures of Sr4−xNb17O26 and Eu4−xNb17O26 were refined using X-ray powder diffraction and neutron diffraction data (only Sr4−xNb17O26). The Rietveld refiniments and microanalyses showed x in Eu4−xNb17O26 to be 0.3(l) while the Sr analogue both x= 0.0(1) and 0.3(1) were found. High resolution electron microscopy studies showed that the compounds frequently contained structural defects. The magnetic susceptibility of Eu4−xNb17O26 (x=0.3) shows a Curie-Weiss behaviour, with a magnetic moment in good agreement with the expected μeff=7.9 μB for Eu2+/ The Sr analogie is temperature-independent paramagnetic at room temperature, Sr4−xNb17O26 (x=0.3) and Eu4−xNb17O26 (x=0.3) are metallic, with a resistivity increasing with temperature.

The red emitting title phosphors are prepared by solid state reaction of stoichiometric mixtures of Y2O3, Eu2O3, CaCO3, and GeO2 (1250 °C, 72 h) and by an EDTA-complexing process from nitric acid solutions of Y2O3, Eu2O3, and CaCO3, EDTA, and ammonia solutions of GeO2 (annealing at 1100 °C, 6 h).

The title compounds are synthesized by solid state reaction of stoichiometric mixtures of SrCO3, Ln2O3 (Ln: Y, Eu—Lu), and amorphous SiO2 (air, alumina boats, 1300 °C, 150—200 h).

The infinite-layer compounds of the (Sr, Ln)CuO 2 family have been prepared by a new synthesis method from the low-pressure phase of SrCuO 2 and NdCuO 2 as starting materials. The crystal structure, microstructure and superconductivity of these samples have been studied with use of neutron powder diffraction, optical micrographs, energy-dispersive X-ray analysis. magnetic-susceptibility and electrical-resistivity measurements. The ratio of the lattice constants a/c as an empirical parameter for the existence of superconductivity in the electron-doped infinite-layer compounds is discussed.

Powder samples of the reduced oxoniobates Eu0.7NbO3, EuNbO3, Eu2Nb5O9, EuNb8O14 and BaNb8O14 have been synthesised. EuNbO3 and Eu0.7NbO3 adopt the perovskite type structure (space group Pm3m) with unit cell parameters a = 4.021(1) and 3.981(3) A , respectively. Eu2Nb5O9 exhibits an intergrowth structure which can be described as alternating slabs of NbO and EuNbO3. It crystallises in P4 mmm with a = 4.131(1) and c = 12.043(5) A . EuNb8O14 and the here synthesised modification of BaNb8O14 is isostructural with SrNb8O14. The structures of EuNb8O14 and BaNb8O14 have been refined from X-ray powder diffraction data with the Rietveld technique. They have the unit cell parameters a = 9.2272(1), b = 10.2647(2), c = 5.9381(1) and a = 9.3451(1), b = 10.2689(2), c = 5.9470(4) A , (space group Pbam), respectively. In all the studied compounds AO12 cuboctahedra (A = Eu, Ba) form either chains (in ANb8O14), double layers (in Eu2Nb5O9) or three-dimensional nets (in EuNbO3 and Eu0.7NbO3). Magnetic susceptibility measurements show temperature independent paramagnetism for BaNb8O14, while the susceptibilities of the Eu niobates follow Curie-Weiss laws with effective magnetic moments in good agreement with the expected μeff = 7.9 μB for Eu2+. Eu0.7NbO3 and Eu1.0NbO3 exhibit ferromagnetic ordering below 4 K. BaNb8O14 and EuNb8O14 are semiconductors, while Eu2Nb5O9, EuNbO3 and Eu0.7NbO3 are metallic.

The new compounds BiCa3La(VO4)2(GeO4)O, BiCa2La2(VO4) (GeO4)2O, and BiCaLa3(GeO4)3O are synthesized by the nitrate—citrate method and characterized by powder XRD, IR, and Raman spectroscopy.