Pressure-induced octahedral tilting distortion and structural phase transition in columbite structured NiNb2O6

Abstract

High-pressure behavior of the technologically important compound NiNb2O6 adopting a columbite-type orthorhombic structure at ambient pressure and temperature conditions was investigated using synchrotron x-ray powder diffraction, Raman spectroscopic measurements, and first-principles calculations. The x-ray diffraction data indicate the occurrence of irreversible pressure-induced structural phase transition in the studied compound beyond 9 GPa. The high-pressure phase is found to be monoclinic with space group P2/m. The large volume collapse (∼4.4%) at the transition indicates the nature of the transition to be of the first order. There is a change in oxygen anion coordination number around Nb from 6 to 8; however, the coordination number around Ni remains 6. The experimental pressure–volume data when fitted to the Birch−Murnaghan equation of states yield the value of ambient pressure bulk modulus (B0) as 178.7 (17) GPa for the orthorhombic phase and 244 (6) for the high-pressure monoclinic phase. The changes in Raman spectra indicate the distortion of NbO6 octahedra resulting in structural phase transitions. The logarithmic variation of unit cell volume (V) with optical lattice mode frequency (ν) helped us to calculate their respective Grüneisen parameters (γ) and it also supports the instability of the orthorhombic columbite structure of NiNb2O6 beyond 9 GPa, originated due to strong octahedral deformation of NbO6 octahedra. The variation of structural, electronic, and optical properties with pressure has also been discussed through first-principles calculations based on density functional theory using the revised Perdew–Burke–Ernzerh of generalized gradient approximation. The theoretical bandgap collapses and the distortion of NbO6 octahedra through the O chains with pressure are emphasized from the density of states data.

Synthesis of Highly Crystalline Single-Phase CoNb2O6 Nanofibers at Low Temperature and Their Structural Characterizations

“…Sharpness of phonon peaks suggests that our samples are of high crystallinity as bulk single crystals. The general features of our observed Raman spectra in electrospun CoNb 2 O 6 are in good agreement with those in other columbite structured crystalline MNb 2 O 6 , − , − , so it demonstrates the same structure and purity in chemical composition. Our Raman results ensure that the electrospun nanofiber samples have excellent crystalline quality.…”

“…In a unit cell, there are eight and four corner-sharing NbO 6 and AO 6 octahedra, in which three inequivalent oxygen sites, namely, O c (chain), O b (bridge), and O t (terminal), exist as illustrated in Figure d. The distinct chemical environments of the three different oxygens are closely related to the local lattice dynamic structure that can be directly characterized by Raman scattering spectroscopy. − Several optical and electrical measurements reported the insulating character of ANb 2 O 6 whose band gaps range around 2–4 eV , depending on the A site metal element, which implies the paramagnetic character of finite d configurations, e.g., Mn 2+ (d 5 ), Ni 2+ (d 8 ), and Co 2+ (d 8 ) with opening the spin gap. , Interestingly, the insulating character and multivalency of A cations in ANb 2 O 6 can be used for applications such as photocatalysis and gas sensors. − In this regard, micrometer or nanometer scale synthesis, for instance, in the form of quantum dots or nanowires and the characterization of the products are highly desirable for wider utility, while most reports of characterization of ANb 2 O 6 are focused on single crystals. ,, …”

Structural Metamorphosis and Band Dislocation of Trirutile NiTa2O6 under Compression

“…The same software was used to convert the two-dimensional rings obtained on the detector to standard one-dimensional intensity vs 2θ plots. These data were used to obtain the structural details through Rietveld analysis using GSAS software …”

“…These data were used to obtain the structural details through Rietveld analysis using GSAS software. 25 Computational Details. We performed all of the firstprinciples calculations based on the density functional theory implemented in the Quantum Espresso package.…”

“…Recently, Jia et al have examined high-pressure XRD and Raman scattering of MgTa 2 O 6 and observed some structural transformation . Moreover, high-pressure structural deformation by in situ XRD and Raman spectroscopy have been observed on some other Nb-based compounds such as MgNb 2 O 6 , MnNb 2 O 6 , and NiNb 2 O 6 . − …”