Synthesis and Structure of a New Family of Nickelates: Tl(Ln2Sr2)Ni2O9, Ln=La, Pr, Nd, Sm, Eu, and Gd

The 11B nuclear magnetic resonance (NMR) spectra, together with X-ray diffraction (XRD) and scanning electron microscopy (SEM), have been used to investigate the phase separation in 15Na2O-85B2O3 binary glass. Based on the present investigation we suggest that the phase equilibrium in sodium borate glasses is controlled by the rate competition of the nucleation and crystal growth between two immiscible phases rather than those being proposed by the conventional phase diagram. The experimental results show that the sodium-rich phase, after being heat-treated at 500°C, was not Na2O .4B2O3, as indicated by phase diagram. The over-coordination of oxygen atoms in the sodium-rich phase rendered difficulties in the crystallization of the sodium-rich phase with less than 75 mol % sodium oxide. Therefore, the high growth rate of the boron-rich phase can force the residual glass toward much higher concentrations of sodium oxide. According to the NMR measurements, it was found that, after reaching equilibrium, the 15Na2O-85B2O3 glass separated into Na2O .9B2O3 and 3Na2O.B2O3.