Understanding the Unusual Response to High Pressure in KBe2BO3F2

D H Yu,Y Liu,T Lu,H Liu,J E Bradby,L Q Huston,D H Sun,M Avdeev,N Yie,Q Gu,Q B Sun,J Y Wang,G J Mcintyre,Thomas B Shiell

doi:10.1038/s41598-017-04323-2

Abstract

Strong anisotropic compression with pressure on the remarkable non-linear optical material KBe2BO3F2 has been observed with the linear compression coefficient along the c axis found to be about 40 times larger than that along the a axis. An unusual non-monotonic pressure response was observed for the a lattice parameter. The derived bulk modulus of 31 ± 1 GPa indicates that KBe2BO3F2 is a very soft oxide material yet with stable structure up to 45 GPa. A combination of high-pressure synchrotron powder X-ray diffraction, high-pressure Raman spectroscopy, and Density Functional Theory calculations points to the mechanism for the unusual pressure response being due to the competition between the K-F bond length and K-F-K bond angle and the coupling between the stretching and twisting vibration modes.

Highlights

From the materials synthesis point of view, large KBBF crystals with thickness greater than 4 mm are very difficult to synthesize using the flux method due to the layered crystal structure
We report our investigation on the high-pressure response of KBBF using synchrotron powder X-ray diffraction (PXRD), Raman Spectroscopy (RS), and Density Functional Theory (DFT) calculations, aiming to provide a better understanding of the mechanism for the NAC property of this material
Synchrotron PXRD patterns were collected from ambient pressure (AP) to 9.7 GPa and

Summary

OPEN Understanding the Unusual

Response to High Pressure in Received: 23 January 2017 Accepted: 15 May 2017 Published: xx xx xxxx. In addition to the unique non-linear optical properties, other new properties of KBBF crystal like negative thermal expansion (NTE), negative area compressibility (NAC), and the associated potential applications such as smart strain conversion and acoustical-optical coupling devices have been explored recently[5, 6]. These abnormal behaviors are believed to be attributed to the concerted structural distortion of the [BeO3F] tetrahedra in the two-dimensional [Be2BO3F2] framework under external stimulus of temperature and/or pressure[6]. We report our investigation on the high-pressure response of KBBF using synchrotron powder X-ray diffraction (PXRD), Raman Spectroscopy (RS), and Density Functional Theory (DFT) calculations, aiming to provide a better understanding of the mechanism for the NAC property of this material

Results and Discussion

Methods

Author Contributions

Additional Information