Czochralski growth of pure and Pr3+-doped CaTiSiO5 and Ca2ZnSi2O7

Pure and Pr3+-doped titanite (GaTiSiO5) single crystals of cm-size were obtained by the Czochralski method. Go-doping with Na+ was necessary to prevent a partial reduction of Ti4+ to Ti3+. The effective distribution coefficients k(eff) were 0.06 for Pr3+ and 0.008 for Na+, respectively. Maximum doping levels of 0.07 mol% Pr3+ and 0.1 mol% Na+ were achieved. Growth of pure hardystonite (Ca2ZnSi2O7) yielded single crystals of 40 mm in length and 10 mm diameter. In this case the evaporation of ZnO led to CaSiO3 inclusions in the core of Pr3+-doped crystals. A k(eff) of 0.03 and a maximum doping level of 0.01 mol% were obtained. The phase diagram near the composition Ca2ZnSi2O7 of the quasi-binary system ZnO-CaSiO3 was reinvestigated by visual determination of the liquidus curve. Titanite and hardystonite crystals were characterized by optical absorption measurements, electron microprobe and inductively coupled plasma optical emission spectroscopy (IGP-OES) analyses.