High‐Pressure/High‐Temperature Synthesis of LnB3.6O7 (Ln=La, Pr) – Two Unique Lanthanoid Borates in a Defective α‐SrB4O7‐Structure‐Type.

The orthorhombic phases LaB3.6O7 and PrB3.6O7 were obtained by high‐pressure/high‐temperature syntheses at 11 GPa and temperatures of 1130 °C (LaB3.6O7) as well as 850 °C (PrB3.6O7) using a modified Walker‐type multianvil apparatus. The title compounds crystallize in the space group Pmn21 (no. 31) exhibiting a defective α‐SrB4O7 structure variant with the unit cell parameters a=10.4551(3) Å, b=4.4562(1) Å, c=4.2973(1) Å for LaB3.6O7 and a=10.4305(3) Å, b=4.4257(1) Å, c=4.2815(1) Å for PrB3.6O7. Both compounds were characterized by powder/single‐crystal X‐ray diffraction, vibrational spectroscopy, second harmonic generation, and electron dispersive X‐ray spectroscopy measurements. [ABSTRACT FROM AUTHOR]