Determination of the phase diagram Tb2O3–SiO2 and crystal growth of the rare earth pyrosilicate Tb2Si2O7 by the optical floating-zone (OFZ) technique

Abstract

By differential thermal analysis (DTA) is was shown that the pseudo-binary system Tb2O3–SiO2 contains intermediate compounds Tb2SiO5, Tb4Si3O12 and Tb2Si2O7. All three compounds melt congruently, a phase diagram was proposed, and from the latter compound single crystals could be grown for the first time. This was possible from stoichiometric feed rods by the optical floating-zone (OFZ) technique. X-ray powder analysis proved the Pna21 phase of the crystals. Melting temperature and heat of fusion were measured by DTA to be 1769◦C and ≈150 kJ/mol, respectively. The specific heat capacity of Tb2Si2O7 was measured by dynamic DSC to be cp ​= ​149.4982 ​+ ​0.2242 ⋅ T − 7.3913 ​× ​10−5 ⋅ T2 + 558449.3624 ⋅ T−2.