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Fundamental studies of the materials with fast sodium mobility are important for the development of energy storage systems. This article presents the results of experimental studies of Na-conducting oxide Na9In(MoO4)6. This compound crystallizes in rhombohedral symmetry with the space group R $$\overline{3}$$ c and the unit cell parameters: a = 15.08695(6) and c = 19.1701(2) A. Impedance spectroscopy measurements show that Na9In(MoO4)6 is an ionic conductor with a conductivity of about 2.1 × 10−2 Sm·cm−1 at 803 K. The 23Na NMR data reveal the coexistence of three types of sodium motion. These motional processes are activated at different temperatures and are characterized by substantially different nature and dynamics characteristics.

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.

The rechargeable Na-ion batteries attract much attention as an alternative to the widely used but expensive Li-ion batteries. The search for materials with high sodium diffusion is important for the development of solid state electrolytes. We present the results of experimental and ab initio studies of the Na-ion diffusion mechanism in Na9Sc(MoO4)6. The ion conductivity reaches the value of 3.6 × 10−2 S cm−1 at T ∼ 850 K. The 23Na and 45Sc NMR data reveal the coexistence of three different types of Na-ion motion in the temperature range from 300 to 750 K. They are activated at different temperatures and are characterized by substantially different dynamics parameters. These features are confirmed by ab initio calculations of activation barriers for sodium diffusion along various paths.

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.

The crystal structure, electronic properties, and sodium diffusion mechanism in Na5Sc(MoO4)4 were investigated using the powder X-ray diffraction, nuclear magnetic resonance, and electrical conduct...

A new series of Ba

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 promising series of phosphors based on Li7La3Hf2O12:xLn3+ (Ln = Tb, Dy) has been prepared using a conventional solid state reaction and their luminescence properties have been investigated. The powder X-ray diffraction patterns show that Li7(La1-xLnx)3Hf2O12 (Ln = Tb, Dy) solid solutions crystallize in the tetragonal space group I41/acd, Z = 8. The photoluminescence spectra of Tb3+ doped Li7La3Hf2O12 contain well-known blue-green emission lines due to the 5D4→7FJ (J = 3–6) transitions of Tb3+. At relatively low activator concentrations, the blue emissions from the 5D3 level are observed along with emissions from the 5D4 level. The intensity ratio between the emission levels of 5D3 and 5D4 depends significantly on the terbium content, which makes it possible to obtain a tunable emission from green to yellowish green color. Under UV excitation, the emission spectra of Li7La3Hf2O12:xDy3+ phosphor exhibit several peaks attributed to the 4F9/2→6HJ (J = 11/2, 13/2 and 15/2) transitions with stable CIE chromaticity coordinates (0.417, 0.420) located in the white light region.

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.

In this paper we report on the stabilization of cubic Li7La3Hf2O12 by Al3+ doping and present a detailed crystal structure study and lithium ion conductivity measurements of the obtained compound. Polycrystalline Al-doped Li7La3Hf2O12 was prepared by a modified solid state method. The compound consists of micrometer size grains encapsulated by a glassy phase, which helps preventing the volatilization of lithium during annealing. Al-doped Li7La3Hf2O12 crystallizes in the garnet-related structure with a cubic unit cell (sp. gr. Ia 3 ¯ d (230)). A structural refinement using X-ray and neutron powder diffraction data showed that the Al3+ ions occupy only tetrahedral Li+ sites in the structure. The presence of overextended leading edges of the peaks on the XRD and NPD data is described by the introduction of an additional phase with rhombohedral distortion that occurs through a stretching of the cubic phase along the body diagonal. The activation energy as well as the total conductivity at room temperature are close to values obtained for un-doped cubic Li7La3Zr2O12 and Li7La3Hf2O12 garnets, which make Al-doped Li7La3Hf2O12 a potential candidate for the application as solid electrolyte in solid-state rechargeable lithium-ion batteries.

A promising series of infrared phosphors Ca3Y2-х-yNdxHoyGe3O12 (x = 0.0–0.3; y = 0.000015–0.15) with garnet structure has been prepared using a liquid-phase precursor method. The room temperature X-ray powder diffraction study and density functional theory (DFT) calculations show consistently that incorporated trivalent neodymium ions occupy calcium dodecahedral sites, whereas ousted part of calcium ions moves into yttrium/holmium octahedral sites. DFT calculations and results of diffuse reflectance measurements reveal that an increase in the neodymium concentration and, consequently, the degree of cation substitution leads to a noticeable band gap reduction. The infrared luminescence in range from 1.0 to 3.4 µm for Ca3Y2-х-yNdxHoyGe3O12 is observed under 808 nm laser diode excitation. The trace amount of holmium ions and a low doping ratio of Ho3+ and Nd3+ ions allow revealing of intense emission at 2.0–3.4 µm region. The highest emission intensity is attained at x = 0.15 in Ca3Y2-хNdxGe3O12:Ho3+. The concentration quenching of Ho3+ emission in the Ca3Y1.85–yNd0.15HoyGe3O12 solid solutions is observed at the activator content of y > 1.5·10−4. A very weak red upconversion emissions at 650 and 740 nm were observed upon 808 nm laser diode excitation. The proposed mechanism for multistage process of energy transfer between the active centers involves the participation of Nd3+ ions as sensitizers of infrared luminescence of Ho3+ ions. The results indicate that the Ca3Y2-х-yNdxHoyGe3O12 germanate can be considered as a promising material for near- and middle infrared phosphors.

The new polycrystalline samples of Li7La3Hf2O12:xCe (x = 0.00–3.30%) with tetragonal garnet structure have been prepared using a conventional solid state reaction. The phase composition, morphology and optical properties of undoped and cerium doped compounds have been characterized by powder X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance, diffuse reflectance and photoluminescence spectroscopy. The absorption bands at 2.5 eV (496 nm) and 3.3 eV (375 nm) are associated with processes of light absorption in F-centers in tetragonal Li7La3Hf2O12. The origin of luminescence in Li7La3Hf2O12 can be explained by the creation and relaxation of self-trapped exciton localized in [HfO6]8- system. The Ce ions in Li7La3Hf2O12:xCe (x = 0.00–3.30%) have predominantly the Ce4+ valence state, and no luminescence of Ce3+ is observed. The increase in the cerium concentration in Li7La3Hf2O12 leads to a reduction of the photoluminescence intensity associated with intrinsic luminescence centers. Using the temperature dependence of luminescence, the activation energy of temperature quenching of intrinsic luminance was calculated.

The apatite-like NaLa9(GeO4)6O2:Nd3+,Ho3+ phosphor is prepared using the solid-state method. Rietveld refinement of high-resolution time-of-flight neutron powder diffraction measurements indicate that this compound crystallizes in the hexagonal system with space group P63/m, Z = 1 and unit cell parameters a = 9.88903(6) A, c = 7.25602(5) A, V = 614.521(7) A3 at room temperature. The 4f sites are statistically occupied by La, Nd and Na, while 6h sites are occupied by La and Nd. Luminescence in the near- and middle-IR range caused by the transitions in neodymium and holmium ions is excited under 808 nm laser diode radiation. The highest emission intensity in NaLa9-x-yNdxHoy(GeO4)6O2 is attained at trace amounts of holmium, and it decreases sharply when y increases to 0.01. The IR phosphors have a good thermal stability and exhibit a very weak upconversion emission in the red spectral range upon 808 nm excitation. A scheme of excitation and emission pathways involving ground/excited state absorption, energy transfer, cross-relaxation, nonradiative multiphonon relaxation processes in Nd3+ and Ho3+ ions has been proposed. The data analysis indicates that Nd3+ ions serve as sensitizers for Ho3+ ions in these compounds, stimulating intense 2.1 μm and 2.7 μm emissions. These apatite-related germanate phosphors are promising materials for near- and middle-infrared solid-state lighting applications.

A new series of Sr3RE2(Ge3O9)2 (RE = La, Pr, Nd, Sm, Eu, Gd) cyclogermanates has been prepared using an ethylenediaminetetraacetic acid assisted route. The powder XRD study reveals that the compounds crystallize in the monoclinic space group C2/c, Z = 4. A decrease in the crystal radius of RE3+ ions in Sr3RE2(Ge3O9)2 (RE = La–Gd) causes a morphotropic phase transition followed by a step-like change of the lattice parameters. The transition is accompanied by internal reorganization, including the redistribution of rare earth and strontium ions among three symmetry independent Sr/RE sites, a conformation change of [Ge3O9]6− rings and a variation of Sr/RE(2) atom coordination from seven-fold to nine-fold. Density functional theory calculations reveal that Sr3RE2(Ge3O9)2 compounds are indirect bandgap materials with a band gap around 3.0 eV. The magnetic property measurements indicate that Sr3RE2(Ge3O9)2 (RE = Pr, Sm, Gd) are Curie–Weiss paramagnets up to 2 K. For Sr3Eu2(Ge3O9)2 an anomaly of magnetic susceptibility is found at about 60 K. A photoluminescence study of the Sr3Sm2(Ge3O9)2 and Sr3Eu2(Ge3O9)2 samples reveals an emission in the visible spectral range, corresponding to the characteristic 4f–4f transitions in rare earth ions.

The new single-phase oxyapatites A La 9 (GeO 4 ) 6 O 2 and A La 8.93 Eu 0.07 (GeO 4 ) 6 O 2 ( A = Li, Rb, space group P 6 3 / m ) are prepared using the ethylenediaminetetraacetic acid (EDTA) assisted process and the solid state method. Detailed characterization of the fine features of electronic structure within the families of oxyapatites A La 9 (GeO 4 ) 6 O 2 and A La 8.93 Eu 0.07 (GeO 4 ) 6 O 2 (A = Li, Na, K, Rb) has been performed using photoluminescence measurements and density functional theory (DFT) calculations. The trivalent europium ions may occupy two crystallographically nonequivalent sites (4 f ) and (6 h ) with the C 3 and C s symmetry, respectively, and can be distinguished using the photoluminescence excitation on and the photoluminescence spectra from potassium and rubidium germanates, in contrast to those for lithium and sodium compounds. All the compounds should be semiconductors with wide direct band gaps of about 3.8 eV for alkali metal derivatives and about 3.2 eV for the vacancy-stabilized La 9.33 (GeO 4 ) 6 O 2 composition. The thermodynamic stability, the lattice parameters and the band gap value of CsLa 9 (GeO 4 ) 6 O 2 not yet synthesized as a single phase have been qualified using DFT calculations.

Simultaneous emission lines around 1.05 μm, 1.3 μm, 1.8 μm, 2.1 μm and 2.7 μm have been observed in Li7La3 − xNdxHf2O12:Ho3 + (x = 0.00–0.15) under 808 nm laser diode excitation. Near-infrared luminescence due to holmium ions with residual concentration in the Li7La3Hf2O12 host has been studied. The intensity of 2.1 and 2.7 μm lines associated with 5I7 → 5I8 and 5I6 → 5I7 transitions in Ho3 + depends on the neodymium codopant concentration. This result indicates that Nd3 + ions can be potentially used as sensitizers for Ho3 + ions to stimulate the intense near-infrared emission in this system. Possible energy transfer mechanisms between lanthanide ions have been briefly discussed.

New cyclogermanates Sr 3 RE 2 (Ge 3 O 9 ) 2 ( RE =La, Y) with Ca 3 Y 2 (Si 3 O 9 ) 2 cyclosilicate structure type have been prepared by two liquid-phase precursor routes: the citrate and the Pechini methods. The phase composition, morphology and optical properties of the intermediate and final products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). The thermogravimetric (TGA) and differential thermal analyses (DTA) were used to study the thermal decomposition of the precursors. The powder XRD measurements indicate that the phase formation of Sr 3 RE 2 (Ge 3 O 9 ) 2 ( RE =La, Y) (S.G. C 2 /c , Z=4) takes place after 20 h annealing at 800 °C. The DRS data revealed that the cyclogermanates are promising optical hosts.

The rechargeable Na-ion batteries attract much attention as an alternative to the widely used but expensive Li-ion batteries. The search for materials with high sodium diffusion is important for the development of solid state electrolytes. We present the results of experimental and ab initio studies of the Na-ion diffusion mechanism in Na9Sc(MoO4)6. The ion conductivity reaches the value of 3.6 × 10-2 S cm-1 at T ∼ 850 K. The 23Na and 45Sc NMR data reveal the coexistence of three different types of Na-ion motion in the temperature range from 300 to 750 K. They are activated at different temperatures and are characterized by substantially different dynamics parameters. These features are confirmed by ab initio calculations of activation barriers for sodium diffusion along various paths.

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.

This paper presents the results of lithium dynamics studies of monoclinic β-Li2HfO3. The 6Li MAS and 7Li static NMR experiments and ab initio calculations have been performed to clarify the features of lithium motion in this layered Li-conducting oxide. It was revealed that two types of lithium motion with significantly different characteristic jump frequencies coexist at 425–900 K. One of the processes, responsible for the long-range lithium diffusion, is characterized by an activation energy of Ea = 1.00 ± 0.05 eV and an ion jump frequency of τd–1 ∼ 104 s–1, at T ∼ 750 K. The long-range lithium diffusion represents the successive ion jumps between the nonequivalent octahedral sites in Li/Hf and Li layers, occurring through the distinct type of tetrahedral interstitials (meanwhile, two other types of tetrahedra are less involved in motion). Another type of ion dynamics is the much more rapid localized motion of Li ions with Ea ∼ 0.6 eV and τd–1 ∼ 104 s–1 already at T ∼ 400 K. The mechanisms of lithium mo...

Alluaudite-type compounds are currently considered as a promising class of materials for sodium-ion batteries, and understanding of the diffusion processes in them is very important. Using the 23Na MAS NMR and ab initio calculations, we established the mechanism of sodium diffusion in Na4–2xM1+x(MoO4)3 (M ​= ​Mg, Zn, Cd) depending on the type of M-element and x. A comparison of the results obtained for various alluaudite-type compounds shows the crucial effect of the M-cation on the Na-ion dynamics in this class of materials. Higher concentration and charge of M-element increase the concentration of vacancies in the Na-sublattice and enhance the sodium mobility. Moreover, the Na dynamics increases with the M-ion size. The occupancy of the M site and the type of T atom in the TO4 group also determine the mechanism of sodium diffusion in alluaudites, whether it is one-dimensional or two-dimensional. These findings may help a deeper understanding of sodium diffusion processes in alluaudite-type compounds and their development as materials for sodium-ion batteries.

New germanate ALa9(GeO4)6O2 (A = Li, Na, K, Rb, Cs) oxyapatites, showing promise as host lattices for phosphors with emission in the visible and infrared spectral ranges, have been obtained for the first time by ultrasonic spray pyrolysis. The discussion is focused on native defectiveness and optical properties of these compounds, depending on the nature of alkaline ions. Spray pyrolysis method was consciously used to obtain the compounds with intrinsic defects as confirmed by electron paramagnetic resonance. Reviewing available EPR data, the registered EPR response was assigned to the paramagnetic centers related to germanium tetrahedra embracing the oxygen vacancies. According to quantum-chemical calculations the oxygen-deficient centers in ALa9(GeO4)6O2 are presumably stabilized by antisite defects in the cation sublattice. Diffuse reflectance and pulse cathodoluminescence spectra of the compounds were investigated in detail, establishing a distinct dependence of optical properties on the type of alkaline ion. The observed optical absorption maxima at 275 and 370 nm were attributed to the F-like centers. The inverse dependence of luminescence intensity on the degree of defectiveness was interpreted on the assumption that these centers were involved in non-radiative energy relaxation.

Alluaudite phases are very attractive as both cathode and electrolyte materials for rechargeable sodium-ion batteries. In this work, the combined experimental and DFT studies have been performed to establish the diffusion mechanism in alluaudite-like compound Na5In(MoO4)4. The ionic conductivity was found to reach 3.3 × 10−4 S/сm at 687 K, with an activation energy of 0.66 eV. The sodium diffusion mechanisms have been revealed from the analysis of the 23Na NMR spectra along with the DFT estimations of Na-ion migration barriers. Our results predict that one-dimensional diffusion of sodium in the separate channels along the c-axis is accompanied by the cross-linking jumps providing two-dimensional diffusion in the bc-plane. It is clearly demonstrated that the indium deficiency favors 2D diffusion, but sharply increases the energy barrier for 1D diffusion. Comparison of our results for Na5In(MoO4)4 and related Na5Sc(MoO4)4 shows that the type and deficiency of M-metal in the NaxMy(MoO4)z alluaudites can control the sodium diffusion. The present work highlights the key aspects of cation influence on the diffusion properties in alluaudite materials.

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 apatite-like NaLa9(GeO4)6O2:Nd3+,Ho3+ phosphor is prepared using the solid-state method. Rietveld refinement of high-resolution time-of-flight neutron powder diffraction measurements indicate that this compound crystallizes in the hexagonal system with space group P63/m, Z = 1 and unit cell parameters a = 9.88903(6) Å, c = 7.25602(5) Å, V = 614.521(7) Å3 at room temperature. The 4f sites are statistically occupied by La, Nd and Na, while 6h sites are occupied by La and Nd. Luminescence in the near- and middle-IR range caused by the transitions in neodymium and holmium ions is excited under 808 nm laser diode radiation. The highest emission intensity in NaLa9-x-yNdxHoy(GeO4)6O2 is attained at trace amounts of holmium, and it decreases sharply when y increases to 0.01. The IR phosphors have a good thermal stability and exhibit a very weak upconversion emission in the red spectral range upon 808 nm excitation. A scheme of excitation and emission pathways involving ground/excited state absorption, energy transfer, cross-relaxation, nonradiative multiphonon relaxation processes in Nd3+ and Ho3+ ions has been proposed. The data analysis indicates that Nd3+ ions serve as sensitizers for Ho3+ ions in these compounds, stimulating intense 2.1 μm and 2.7 μm emissions. These apatite-related germanate phosphors are promising materials for near- and middle-infrared solid-state lighting applications.

Solid electrolytes are important materials with a wide range of technological applications. This work reports the crystal structure and electrical properties of a new solid electrolyte Na9Al(MoO4)(6). The monoclinic Na9Al(MoO4)(6) consists of isolated polyhedral, [Al(MoO4)(6)](9-) clusters composed of a central AlO6 octahedron sharing vertices with six MoO4 tetrahedra to form a three-dimensional framework. The AlO6 octahedron also shares edges with one NalO(6) octahedron and two Na2O(6) octahedra. Na3-Na5 atoms are located in the framework cavities. The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)(3). High-temperature conductivity measurements revealed that the conductivity (sigma) of Na9Al(MoO4)(6) at 803 K equals 1.63 X 10(-2) S cm(-1). The temperature behavior of the Na-23 and Al-27 nuclear magnetic resonance spectra and the spin-lattice relaxation rates of the Na-23 nuclei indicate the presence of fast Na+ ion diffusion in the studied compound. At T

The crystal structure of a new hafnium oxyhydroxide obtained by an ion-exchange reaction from a Li2HfO3 precursor has been solved by a direct method and refined using Rietveld full profile fitting based on X-ray powder diffraction data. HfO(ОН)2 crystallizes in a P21/c monoclinic unit cell (a = 5.5578(5) Å, b = 9.0701(10) Å, c = 5.7174(5) Å, β = 119.746(5)°); its structure can be described as a framework formed by edge-sharing HfO6 octahedra connected to each other via vertices. In addition, an analysis of the atomic pair distribution function obtained using synchrotron radiation was used to confirm the model and to describe fine-structure features.

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.

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li

Complex lithium metallates Li2MexZr1 − xO3 − δ (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr4+ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti4+ and Nb5+ ions in the crystal structure of Li2ZrO3 is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li2Ti0.1Zr0.9O3 solid solution has higher conductivity than phases of undoped lithium zirconate.

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.

Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2(1)/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.

Crystal structures of Li2MO3 (M=Sn, Ti) and TiO(OH)2 have been studied in detail and refined using X-ray powder diffraction data. All compounds posses a high concentration of defects in the structure. The crystal structures of the Li2MO3 salts obtained at 700°C reveal stacking faults of LiM2 metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3112. The possibility to stabilize this imperfect state increases the mobility of the Li+ ions in the Li2TiO3 structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)2. The crystal structure of TiO(OH)2 belongs to the layered double hydroxide structure type with the 3R1 sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)2OTi2O(OH)2].

Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.