The structural and magnetic properties of a glaserite-type NaBaFe(VO) compound, featuring a triangular magnetic lattice of Fe (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal P3̅m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T = 288 K). This structural transition involves a tilting of Fe-O-V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in NaBaFe(VO). The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Overall, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO octahedron.

A convenient hydrothermal route to high quality single crystals of rare earth orthoniobates RENbO 4 (RE = Y, La−Lu) is reported. The title compounds can be grown as single crystals in sizes exceeding 2 mm for most of the rare earths using 30 M KOH at temperatures of 700 °C and pressures of 2 kbar. Single crystal X-ray diffraction shows that they all form in the fergusonite structure type, and the structures were solved in space group C2/c. Examples based on the largest and smallest rare earth ions in the present study include LaNbO 4 : a = 7.3576( 15) Å, b = 11.538(2) Å, c = 5.2128(10) Å, β = 130.900(3)°, Z = 4, R 1 = 0.0162, wR 2 = 0.0405, and LuNbO 4 : a = 6.9805(6) Å, b = 10.8271(8) Å, c = 5.0406(4) Å, β = 131.676(3)°, Z = 4, R 1 = 0.0178, wR 2 = 0.0489. Although domain structures are clearly present in the bulk crystals, the domains are much larger than normally reported from high temperature growth methods, and individual single domain crystals on the order of 0.1−1 mm in size can be selected. Rocking curves of these crystals have narrow fwhm and are Gaussian shaped. Several new phases were also isolated as part of the development of the crystal growth chemistry and were characterized by single crystal X-ray diffraction including such examples as K 3 YNb 2 O 7 (OH) 2 : P6 3 / mmc, a = 5.9770(12) Å, c = 14.901(2) Å, Z = 2, R 1 = 0.0303, wR 2 = 0.0765 and CsNb 2 O 5 (OH): Fd3̅ m, a = 10.5869(14) Å, Z = 8, R 1 = 0.0336, wR 2 = 0.0741.

A series of new lanthanide (Ln) silicates have been synthesized using high temperature hydrothermal techniques, and structurally characterized using single crystal and powder X-ray diffraction. The compounds have the general formula NaBa 3 Ln 3 Si 6 O 20 (Ln = Y, Nd, Sm, Eu, Gd), and crystallize in the space group Ama2 (No.40). As a representative example, the unit cell parameters of NaBa 3 Gd 3 Si 6 O 20 are a = 14.731(3) Å, b = 23.864(5) Å, c = 5.5449(11) Å and Z = 4. The title compounds adopt a three dimensional polar acentric framework made of Ln−O−Si bonding. The framework is comprised of LnO 8 and LnO 7 units forming edge-sharing infinite chains along the c-axis. These oxy-bridged infinite chains are also linked by [Si 4 O 13 ] tetrasilicate and [Si 2 O 7 ] disilicate units to form the three-dimensional framework structure, with Ba 2+ and Na + cations residing inside channels of the framework. The polarity in the structure is imparted by the unusual tetrasilicate arrangement. The luminescence and magnetic properties were investigated on selected compounds. The temperature dependent magnetic susceptibility measurements on the Nd, Sm, and Gd derivatives reveal a Curie-Weiss behavior with an antiferromagnetic coupling parameter. For the Eu-derivative, the temperature dependent magnetic susceptibility deviates significantly from Curie-Weiss behavior. Luminescence properties of NaBa 3 Eu 3 Si 6 O 20 and NaBa 3 Sm 3 Si 6 O 20 compounds exhibited the characteristic transitions of Eu 3+ (5 D 0 → 7 F J , J = 0-4) and Sm 3+ (4 G 5/2 → 6 H J , J = 5/2, 7/2), respectively, leading to strong visible red and orange emissions, respectively.

Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using TbO as a starting material. Tb(GeO)O(OH) crystallizes in trigonal space group R3̅, is built up of isolated GeO units, and contains a complex arrangement of terbium oxide polyhedra. KTbGeO is a terbium(4+) pyrogermanate that is isostructural with KZrGeO and displays a rare stable Tb oxidation state in the solid state.

New structure types Ln2TaO5(OH) and Ln3Ta2O9(OH) are prepared via hydrothermal synthesis from refractory oxide precursors.