Structure of Ba2Cu(BO3)2

As part of our program in the synthesis and characterization of new solid-state borates, we recently synthesized the polymorphic compound Sr2Cu(BO3)2 (Smith & Keszler, 1989) which undergoes a first-order phase transition from a low-temperature form to a high-temperature form at 1073 K. The high-temperature beta form exhibits larger coordination numbers for the Sr atoms and a substantial rearrangement of the copper borate network relative to that of the low-temperature... form