Yana V. Baklanova

Defect crystal structure of new TiO(OH)2 hydroxide and related lithium salt Li2TiO3

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.

Nd3 +, Ho3 +-codoped garnet-related Li7La3Hf2O12 phosphor with NIR luminescence

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li7La3-xNdxHf2O12:Ho3+ (x=0.00-0.15) under 808nm 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 2.7μm 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.

Short CommunicationNd3 +, Ho3 +-codoped garnet-related Li7La3Hf2O12 phosphor with NIR luminescence

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li7La3-xNdxHf2O12:Ho3+ (x=0.00-0.15) under 808nm 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 2.7μm 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.

Defect Crystal Structure of Low Temperature Modifications of Li2MO3 (M=Ti, Sn) and Related Hydroxides

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].

Synthesis and physicochemical properties of Li2MexZr1 − xO3 − δ (Me = Nb, Ti; x = 0.05, 0.1) solid solutions

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.

Structure, magnetic and optical properties of Sr3RE2(Ge3O9)2 cyclogermanates (RE = La–Gd)

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.