STABILIZATION OF THE RHOMBOHEDRAL PHASE IN LIZR2(PO4)3 BY THERMAL QUENCHING

Two LiZr2(PO4)3 samples, which show rhombohedral and monoclinic symmet ries, have been studied by powder XRD and MAS-NMR (P-31 and Li-7) tech niques. In the monoclinic sample phosphorus occupies three crystallogr aphic sites and lithium is preferentially placed in M2 environment. Wh en the samples are subjected to successive heating-quenching treatment s, the rhombohedral phase is not appreciably modified while the monocl inic phase is transformed into the rhombohedral one. In the quenched s amples only one site for phosphorus has been detected and occupancy of lithium in the more symmetric M1 site is favoured. After the thermal treatments, when the samples are stored at room temperature for one ye ar, the framework does not relax to that of the monoclinic phase but d istribution of lithium changes towards a statistical occupancy of M1 a nd M2 sites.