Structural Transition of MnNb₂O₆ under Quasi-Hydrostatic Pressure

Abstract

High-pressure Raman scattering and X-ray diffraction studies on manganese niobate (MnNb 2 O 6 ) have been carried out in a diamond anvil cell at room temperature up to 41 GPa. A pressure-induced phase transition was observed at 12 GPa accompanied by the softening of two internal vibration modes ν 10 (B 2g ) and ν 8 (A g ). Disappearing of most Raman vibration peaks under high pressure reveals that the NbO 6 octahedra distort heavily through the transition; this is evidenced by the Xray diffraction results, but the octahedral units still exist, as the internal Nb−O strengthening vibration is observable even at the highest pressure in this study. The equation of state for MnNb 2 O 6 in low pressure phase I was obtained with third-order Birch−Murnaghan method, yielding a zero-pressure bulk modulus B 0 and its pressure derivative B 0 ′ of 154.4 ± 3.5 GPa and 4.1, respectively. The volume dependencies of the optical lattice mode frequencies and their respective Gruneisen parameters were extracted; it is suggested that the instability of the columbite orthorhombic structure at high pressure is related to the strong deformation of the NbO 6 octahedra. Decompression measurements suggest that the pressure-induced transformation is partly reversible.

Pressure-Induced Phase Transition in Mn(Ta,Nb)2O6: An Experimental Investigation and First-Principle Study

“…The (Mn,Fe)­(Nb,Ta) 2 O 6 family of compounds encompass two different solid solution series, named tantalite-columbite with orthorhombic structure and tapiolite-mossite with tetragonal structure, the compositional fields were presented in literature, of which the manganotantalite Mn­(Ta,Nb) 2 O 6 belongs to tantalite–columbite series. , They are the most important economic minerals containing base metals: Ta and Nb. In a stable state, manganotantalite shows a columbite-type structure that crystallizes in orthorhombic symmetry with space group of Pbcn , in which edge-sharing [AO 6 ] and [BO 6 ] octahedra chains run parallel along the c -axis. , There are other four synthetic polymorphs of MnTa 2 O 6 formed at different temperatures and pressures, which have trirutile, wolframite, wodginite, and modulated α-PbO 2 structures, respectively . Previous studies have focused on the properties of (Mn,Fe)­(Nb,Ta) 2 O 6 compounds at ambient and high-temperature conditions. − It is reported that the changes in thermal expansion coefficients of unit cell parameters revealed anisotropic expansion behaviors of FeNb 2 O 6 , FeTa 2 O 6 , and MnTa 2 O 6 with temperature. ,, The thermodynamic research shows that FeNb 2 O 6 undergoes a phase transition from orthorhombic to tetragonal structure at 1630 K …”

FeNb2O6/reduced graphene oxide composites with intercalation pseudo-capacitance enabling ultrahigh energy density for lithium-ion capacitors

“…36 In addition, peaks are located below 400 cm À1 , corresponding to Fe-O or O-Nb-O bonds. 37,38 The surface chemical composition of FNO/rGO was characterized via XPS analyses. Fig.…”

Structural properties and Raman spectra of columbite-type NiNb$_{2-x}$V$_x$O$_6$ synthesized under high pressure

“…the two extreme compounds of the series NiNb 2−x V x O 6 are presented in the second and nineth columns of Table 6. As there are no theoretical studies on the normal coordinate analysis of the AB 2 O 6 compounds with the columbite structure when B = V, the identification of the symmetry of the modes presented in the first column of Table 6 was done by comparing our results with those of Raman studies performed in niobates of the AB 2 O 6 family already reported in the literature [20,21,23,24]. Raman spectra acquired for the complete series of NiNb 2−x V x O 6 samples at room temperature and pressure are presented together in Fig.…”