Abstract
In this work, we used Raman spectroscopic and optical absorption measurements and first-principles calculations to unravel the properties of wolframite-type ScNbO4 at ambient pressure and under high pressure. We found that monoclinic wolframite-type ScNbO4 is less compressible than most wolframites and that under high pressure it undergoes two phase transitions at ∼5 and ∼11 GPa, respectively. The first transition induces a 9% collapse of volume and a 1.5 eV decrease of the band gap energy, changing the direct band gap to an indirect one. According to calculations, pressure induces symmetry changes (P2/c–Pnna–P2/c). The structural sequence is validated by the agreement between phonon calculations and Raman experiments and between band structure calculations and optical absorption experiments. We also obtained the pressure dependence of Raman modes and proposed a mode assignment based upon calculations. They also provided information on infrared modes and elastic constants. Finally, noncovalent and charge analyses were employed to analyze the bonding evolution of ScNbO4 under pressure. They show that the bonding nature of ScNbO4 does not change significantly under pressure. In particular, the ionicity of the wolframite phase is 61% and changes to 63.5% at the phase transition taking place at ∼5 GPa.
Highlights
During the past decade, great interest from both ftuenrdnaamryeMntaTlOan[4] doxaipdpelsiehdarveeseaatrtrcahc.1te−d4understanding of their responses to the application of pressure and other external fields is not fully known.Fundamental research is motivated by the need to systematically understand the properties of these compounds and their relationship with chemical bonding.[1−4] On the other hand, from the application point of view, many studies are driven by the multiple technological applications of MTO4 oxides, which range from photocatalytic applications to uses as laser host and scintillating materials.[1−4] Among MTO4 oxides, one of the most interesting groups is formed by wolframite-type compounds.[5]
We will use space group P2/c to describe it, because it is the usual description of wolframites[5] and the standard setting according to the International Union of Crystallography
We have reported an accurate characterization of the properties of ScNbO4 at ambient pressure and under high pressure up to 18 GPa
Summary
Great interest from both ftuenrdnaamryeMntaTlOan[4] doxaipdpelsiehdarveeseaatrtrcahc.1te−d4understanding of their responses to the application of pressure and other external fields is not fully known.Fundamental research is motivated by the need to systematically understand the properties of these compounds and their relationship with chemical bonding.[1−4] On the other hand, from the application point of view, many studies are driven by the multiple technological applications of MTO4 oxides, which range from photocatalytic applications to uses as laser host and scintillating materials.[1−4] Among MTO4 oxides, one of the most interesting groups is formed by wolframite-type compounds.[5]. Great interest from both ftuenrdnaamryeMntaTlOan[4] doxaipdpelsiehdarveeseaatrtrcahc.1te−d4. Understanding of their responses to the application of pressure and other external fields is not fully known. Fundamental research is motivated by the need to systematically understand the properties of these compounds and their relationship with chemical bonding.[1−4] On the other hand, from the application point of view, many studies are driven by the multiple technological applications of MTO4 oxides, which range from photocatalytic applications to uses as laser host and scintillating materials.[1−4] Among MTO4 oxides, one of the most interesting groups is formed by wolframite-type compounds.[5] These ternary oxides are isomorphic to natural iron manganese tungstate, the mineral wolframite. The M cations are bonded to six oxygen atoms to form distorted MO6 octahedral units that share corners with six equivalent TO6 octahedral units and edges with two equivalent MO6 octahedra.
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