Understanding the Unusual Response to High Pressure in KBe2BO3F2

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.

Composite of K-doped (NH4)2V3O8/graphene as an anode material for sodium-ion batteries

The K-doped (NH₄)₂V₃O₈/graphene electrode exhibited stable cycling and a good rate performance.