High-Pressure Synthesis and Characterization of the Ammonium Yttrium Borate (NH₄)YB₈O₁₄

The first high-pressure yttrium borate (NH₄)YB₈O₁₄ was synthesized at 12.8 GPa/1300 °C using a Walker-type multianvil module. The compound crystallizes in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 17.6375(9), b = 10.7160(5), and c = 4.2191(2) Å. (NH₄)YB₈O₁₄ constitutes a novel structure type but exhibits similarities to the crystal structure of β-BaB₄O₇. X-ray single-crystal and powder diffraction, EDX, vibrational spectroscopy as well as quantum chemical calculations were used to characterize (NH₄)YB₈O₁₄.