X-ray study of the synthesis of boron oxides at high pressure: Phase diagram and equation of state

Abstract

A systematic study of the of boron/oxygen systems at high pressure and high temperature has been made using the diamond anvil cell and the Paris-Edinburgh large volume press. The phase diagrams at $3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ are determined from in-situ x-ray measurements. The synthesis of ${\mathrm{B}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{B}}_{6}\mathrm{O}$ only have been observed. No evidence was seen in these experiments for the previously reported ${\mathrm{B}}_{2}\mathrm{O}$ compound over the range of pressures and temperatures studied, $Pl43\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $Tl2500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The equations of state of orthorhombic ${\mathrm{B}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{B}}_{6}\mathrm{O}$ have also been measured in quasihydrostatic medium to pressures exceeding $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Implications for high-pressure material synthesis are discussed.