Title: First non-icosahedral boron allotrope synthesized at high pressure and high temperature,
Abstract: Theoretical predictions of pressure-induced phase transformations often
become long-standing enigmas because of limitations of contemporary available
experimental possibilities. Hitherto the existence of a non-icosahedral boron
allotrope has been one of them. Here we report on the first non-icosahedral
boron allotrope, which we denoted as {\zeta}-B, with the orthorhombic
{\alpha}-Ga-type structure (space group Cmce) synthesized in a diamond anvil
cell at extreme high-pressure high-temperature conditions (115 GPa and 2100 K).
The structure of {\zeta}-B was solved using single-crystal synchrotron X-ray
diffraction and its compressional behavior was studied in the range of very
high pressures (115 GPa to 135 GPa). Experimental validation of theoretical
predictions reveals the degree of our up-to-date comprehension of condensed
matter and promotes further development of the solid state physics and
chemistry.