Phase Relations in the Ln 2 O 3 -Cr 2 O 3 -B 2 O 3 ( Ln = Gd-Lu) Ternary Oxide Systems.

In this work, isothermal sections of the O-CrO-BO ( = Gd-Lu) ternary oxide systems at 900, 1000, and 1100 °C were constructed by determining the phase relations by using a powder X-ray diffraction technique. As a result, these systems were divided into subsidiary subsystems. Two types of double borates, Cr(BO) ( = Gd-Er) and Cr(BO) ( = Ho-Lu), were observed in the investigated systems. Regions of phase stability for Cr(BO) and Cr(BO) were determined. It was shown that the Cr(BO) compounds crystallized in rhombohedral and monoclinic polytype modifications up to 1100 °C; above this temperature and up to the melting points, the monoclinic modification was predominantly formed. The Cr(BO) ( = Gd-Er) and Cr(BO) ( = Ho-Lu) compounds were characterized by using a powder X-ray diffraction method and thermal analysis.