Experimental and theoretical study of SbPO4 under compression

TL;DR

This study combines experimental and theoretical methods to analyze the high-pressure structural and vibrational properties of SbPO4, revealing its high compressibility, anisotropic behavior, and pressure-induced phase transitions.

Contribution

It provides the first joint experimental and theoretical analysis of SbPO4 under high pressure, highlighting its exceptional compressibility and structural transformations.

Findings

SbPO4 is highly compressible among phosphates.

Compression is anisotropic, mainly along the a-axis.

Reversible phase transition occurs above 9 GPa.

Abstract

SbPO4 is a complex monoclinic layered material characterized by a strong activity of the non-bonding lone electron pair (LEP) of Sb. The strong cation LEP leads to the formation of layers piled up along the a-axis and linked by weak Sb-O electrostatic interactions. In fact, Sb is 4-fold coordination with O similar to what occurs with the P-O coordination, despite the large difference of ionic radii and electronegativity between both elements. Here we report a joint experimental and theoretical study of the structural and vibrational properties of SbPO4 at high pressure. We show that SbPO4 is not only one of the most compressible phosphates but also one of the most compressible compounds of the ABO4 family. Moreover, it has a considerable anisotropic compression behavior with the largest compression occurring along a direction close to a-axis and governed by the compression of the LEP and the weak inter-layer Sb-O bonds. The strong compression along the a-axis leads to a subtle modification of the monoclinic crystal structure above 3 GPa leading from a 2D to a 3D material. Moreover, the onset of a reversible pressure-induced phase transition is observed above 9 GPa, which is completed above 20 GPa. We propose that the high-pressure phase is a triclinic distortion of the original monoclinic phase. The understanding of the compression mechanism of SbPO4 can aid in understanding the importance of the ion intercalation and catalytic properties of this layered compound.