Negative thermal expansion properties in tetragonal NbPO5 from the first principles studies

Tao Li,Fei Wang,Dahu Chang,Xiaonan Fu,Qiang Sun

doi:10.1063/1.4977874

Abstract

By using the first-principles calculations based on density functional theory combined with quasi-harmonic approximation, we have studied the geometric structural, thermal properties, and the negative thermal expansion (NTE) properties of tetrahedral NbPO5. The variations of cell parameter and cell volume of tetrahedral NbPO5 with temperature show that it displays NTE behavior in the range of 473-800 K along a-axis and the corresponding average coefficient of thermal expansion (CTE) is approximately -0.766 ×10−6 K−1, while the c cell parameter and the cell volume display positive thermal expansion behaviors. These results are in consistent well with the experiment observations. Further vibrational modes analysis, together with Grüneisen parameters calculations, revealed that the transverse vibration of O corner atoms accompanying the rocking motions of corner-shared NbO6 octahedron and PO4 tetrahedron dominate the negative thermal properties of tetrahedral NbPO5. Our findings will provide an understanding for the underlying mechanisms of the NTE in oxides materials.

Highlights

Negative thermal expansion (NTE) has attracted extensive attention since the discovery of material ZrW2O8 in 1996 by Sleight.[1]
The NbO6 octahedron and PO4 tetrahedron are connected by sharing the O corner atoms
The geometric structural, phonon and thermodynamic as well as negative thermal expansion property of tetrahedral NbPO5 in space group P4/nmm have been studied by using first-principles calculation combined with quasi-harmonic approximation (QHA)

Summary

INTRODUCTION

Negative thermal expansion (NTE) has attracted extensive attention since the discovery of material ZrW2O8 in 1996 by Sleight.[1]. The big pentagonal tunnels, which are formed by three octahedrons and two tetrahedrons, permit small atoms or particles to pass through. These compounds can be used as intercalation materials such as Li-batter anode or catalyst materials.[14]. NbPO5 is a representative material of ABO5 family and was studied extensively by experiment. It has three different phases, which are monoclinic and orthorhombic as well as tetragonal structure. Through the analysis of vibrations of phonon modes, the NTE of NbPO5 attributes to the transverse vibration of O corner atom accompanying the rocking motions of the corner-shared NbO6 octahedrons and PO4 tetrahedrons. This work is helpful for the future application of NbPO5 and understanding the underlying NTE mechanism in oxides materials

COMPUTATIONAL DETAILS

Phonon and thermodynamic properties

The mechanism of NTE

SUMMARY