Nonstoichiometric Ellenbergerite-Type Phosphates: Hydrothermal Synthesis, Crystal Chemistry, and Magnetic Behavior

Abstract

We synthesized single crystals of Na 0.55 Ni 6 (OH) 3 (H 0.61 PO 4 ) 4 (I) and polycrystals of (Na, Ni) 0.64 Ni 5.68 (OH) 3 (H 0.67 PO 4 ) 4 (II) with ellenbergeritelike structures using the hydrothermal method. The phases crystallize in the hexagonal space group P6 3 mc with the following unit cell parameters: a = 12.5342(1) Å, c = 4.9470(1) Å, and V = 673.08(2) Å 3 for I; a = 12.4708(2) Å, c = 4.9435(2) Å, and V = 665.82(2) Å 3 for II; and Z = 2. Their crystal structures are based on a 3D framework built from NiO 6 octahedra and PO 4 tetrahedra. The difference between I and II lies in the way the structural channels are filled along the [001] direction. These channels accommodate segments of Na-and (Na, Ni)centered chains of face-sharing octahedra in the structures I and II, respectively. The magnetic susceptibility χ and the specific heat C p evidence pronounced low-dimensional magnetic behavior at elevated temperatures and the formation of the weakly ferromagnetic long-range order at T N I = 61 K and T N II = 63 K. Analysis of the χ(T) data within both chain and dimer spin models allows the estimation of the leading exchange interaction parameters in the compounds under study.

Synthesis, Structures, and Magnetic Investigations of Nickel Phosphates: Ni2(PO4)(OH), Ni7(PO4)3(HPO4)(OH)3, and NaNiPO4 Including Potential Haldane Behavior

“…Compound II is a novel ellenbergerite-type structure crystallizing in the polar space group P 6 3 mc . The structures of several ellenbergerite, phosphoellenbergerite, and arsenoellenbergerite analogs have been reported from natural and synthetic samples. ,,,, The structure of II features a nickel oxide chain substructure (Figure ) with similarities to I . In II , one unique Ni(1) atom forms parallel chains of face-sharing dimers (Ni···Ni = 2.8243(12) Å) connected to each other via edge-sharing (Ni···Ni = 2.9704(7) Å) and propagating along the c -axis.…”

“…The structures of several ellenbergerite, phosphoellenbergerite, and arsenoellenbergerite analogs have been reported from natural and synthetic samples. 11,21,22,36,37 The structure of II features a nickel oxide chain substructure (…”

“…Phosphates are quite common metal-containing minerals but are still somewhat underdeveloped as a building block in synthetic metal ion chains. A recent study of nonstoichiometric ellenbergerite-type phosphates suggests the synthetic chemistry and magnetic properties in these systems is quite rich . Fortunately, metal phosphates are also well suited for the high-temperature hydrothermal approach.…”

“…A recent study of nonstoichiometric ellenbergerite-type phosphates suggests the synthetic chemistry and magnetic properties in these systems is quite rich. 11 Fortunately, metal phosphates are also well suited for the hightemperature hydrothermal approach. Phosphates also offer an entry point to then explore the direct isoelectronic comparison to arsenates and vanadates, which surprisingly often display quite different magnetic behavior.…”

Crystal structure, infrared spectroscopy and thermodynamic properties of a manganese member of the ellenbergerite family

“…All studied representatives of the discussed families exhibit interesting magnetic properties. For example, Co 6 (OH) 3 (TeO 3 ) 4 (OH) Â 0.9(H 2 O) shows the metamagnetic behavior with three different subsequent canted antiferromagnetic states below T N = 75.5 K. 3 Recently studied Ni-based ellenbergerite-like phosphates demonstrate low-dimensional magnetic behavior at elevated temperatures and the formation of a weakly ferromagnetic long-range order at T N B 60 K. 4 Similar weak ferromagnetic behavior is inherent to the majority of Ni and Co-containing phosphates and arsenates. [5][6][7] However, the magnetic properties of Mn-ellenbergerite-like analogues are still poorly understood.…”