Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba2M(VO4)2(OH), M = V3+, Mn3+, and Fe3+, with Interesting Jahn–Teller and Spin-Liquid Behavior

Lamellar Crystal Structure and Haldane Magnetism in NH4 VPO4 OH

A novel vanadium hydroxide-phosphate, NH4 VPO4 OH, was synthesized hydrothermally in V2 O5 -NH4 H2 PO4 -citric acid system at 230 °C. It was characterized by XRD, TG-DSC, SEM-EDX, FTIR and NMR spectroscopy. NH4 VPO4 OH is isostructural with NH4 GaPO4 OH and features edge-sharing chains of VO6 octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first-principles calculations, NH4 VPO4 OH presents a rare case of Haldane spin system with spin S=1 based on V3+ ions.

NaCo2(SeO3)2(OH): competing magnetic ground states of a new sawtooth structure with 3d7 Co2+ ions

We report the high-pressure synthesis and a comprehensive study of NaCo2(SeO3)2(OH) sawtooth chain structure using bulk magnetic properties and neutron scattering.

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO4)(OH): A Structure with a Quasi One-Dimensional Magnetic Chain

A new member of the descloizite family, a cobalt vanadate, SrCo(VO₄)(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO₄)(OH) crystallizes in the orthorhombic crystal system in space group P2₁2₁2₁ with the following unit cell parameters: a = 6.0157(2) Å, b = 7.645(2) Å, c = 9.291(3) Å, V = 427.29(2) ų, and Z = 4. It contains one-dimensional Co-O-Co chains of edge-sharing CoO₆ octahedra along the a-axis connected to each other via VO₄ tetrahedra along the b-axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO₄)(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co²⁺ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO₆ octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a-axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO₄)(OH).

Single crystal neutron and magnetic measurements of Rb2Mn3(VO4)2CO3 and K2Co3(VO4)2CO3 with mixed honeycomb and triangular magnetic lattices

Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P3[combining macron]1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Néel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear 'up-up-down' fashion, followed by a planar 'Y' type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie-Weiss fit (200-350 K) gives a Curie-Weiss temperature of -42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.

Two spin-canted antiferromagnetic orderings and a field-induced metamagnetic transition in SrMn2(VO4)2(H2O)2

A new vanadate SrMn2(VO4)2(H2O)2 was synthesized and characterized by single-crystal X-ray analysis. It crystallizes in the monoclinic system with space group C2/m, and exhibits a quasi-one-dimensional (1D) structure. The Mn2+ ions form infinite linear-chains along the b-axis through edge-sharing oxygen atoms and further the linear-chains are connected by VO4 polyhedra into a layer in the ab-plane with Sr2+ ions residing in the space between the layers. Magnetic measurement results show that SrMn2(VO4)2(H2O)2 possesses two spin-canted antiferromagnetic orderings at ∼45 K and ∼7 K. The first ordering at ∼45 K possibly corresponds to a small deviation of spins from a strictly antiparallel arrangement. As the temperature decreases, further spin rotations occur leading to a steadier noncollinear antiferromagnetic phase, leading to the second ordering at ∼7 K. Also, a field-induced transition is observed at a critical field (0.4 T) below ∼7 K.

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties

Two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions.

Investigation of a Structural Phase Transition and Magnetic Structure of Na2BaFe(VO4)2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

The structural and magnetic properties of a glaserite-type Na₂BaFe(VO₄)₂ compound, featuring a triangular magnetic lattice of Fe²⁺ (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_s = 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 Na₂BaFe(VO₄)₂. 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 FeO₆ octahedron.

Synthesis, characterization, and mechanism analysis of S = 2 quasi-one-dimensional ferromagnetic semiconductor Pb2Mn(VO4)2(OH)

A brackebuschite-type compound Pb2Mn(VO4)2(OH) was synthesized by a hydrothermal method. Single crystal X-ray diffraction reveals that Pb2Mn(VO4)2(OH) crystallizes in the space group P21/m, with the structure built of single [010] chains of edge-shared MnO6 octahedra bridged by VO4-PbO6 groups along a and c axes, as a result forming a very large inter-chain distance of about 7.67 Å. The magnetic and optical measurements indicate that Pb2Mn(VO4)2(OH) is an S = 2 quasi-one-dimensional ferromagnetic semiconductor, with a very small specific value of intra- and inter-chain exchange coupling Jintra/Jinter = 10(-3), and a band gap of 1.72 eV. The electronic structure calculations indicate that a 90° Mn-O-Mn dpσ-dpσ correlation superexchange dominates the intra-chain ferromagnetic coupling in Pb2Mn(VO4)2(OH).

Hydrothermal synthesis as a route to mineralogically-inspired structures

Mineralogically-inspired hydrothermal synthesis provides a wealth of interesting opportunities for the solid-state inorganic chemist.