Oxonium Ions Substituting Cesium Ions in the Structure of the New High-Pressure Borate HP-Cs1− x(H3O) xB3O5 ( x=0.5-0.7).

The new high-pressure borate HP-Cs_{1− x}(H₃O) _xB₃O₅ ( x=0.5-0.7) was synthesized under high-pressure/high-temperature conditions of 6 GPa/900 °C in a Walker-type multianvil apparatus. The compound crystallizes in the monoclinic space group C2/ c ( Z=8) with the parameters a=1000.6(2) , b=887.8(2), c=926.3(2) pm, β=103.1(1)°, V=0.8016(3) nm³, R1=0.0452, and wR2=0.0721 (all data). The boron-oxygen network is analogous to those of the compounds HP-MB₃O₅, (M=K, Rb) and exhibits all three structural motifs of borates-BO₃ groups, corner-sharing BO₄ tetrahedra, and edge-sharing BO₄ tetrahedra-at the same time. Channels inside the boron-oxygen framework contain the cesium and oxonium ions, which are disordered on a specific site. Estimating the amount of hydrogen by solid-state NMR spectroscopy and X-ray diffraction led to the composition HP-Cs_{1− x}(H₃O) _xB₃O₅ ( x=0.5-0.7), which implies a nonzero phase width. [ABSTRACT FROM AUTHOR]