Instability model of the NaZr2(PO4)3 Structure

ABSTRACTIncorporation of paramagnetic species in NaZr2(PO4)3 (NZP) single crystal made possible to investigate local distortion of the NZP structure from EPR data. Cr3+ and Fe3+ ions were used as paramagnetic probes. We mapped invariant sum of cubic component of the fourth rank tensor of crystal field, the indicative surface of the B04 element of this tensor as well as 2nd, 3rd, and 4th orders axles of the cubic component of the same tensor. From these data the coordination polyhedron of the ion-probe has been modeled and direction to charge compensator has been determined. Based on the coordination polyhedron model obtained it has been shown how would the local symmetry be lowered from C3 (initial symmetry of the Zr-polyhedron) to C1 (Zr substitute ion-probe). A comparison of dynamics of the structure occurring at lowering the symmetry with allowed dynamics of the NZP structure (Roy -Alamo-Agrawal model) makes easily explainable why the dynamics observed results in an instability of the NZP structure and breaking the symmetry from R 3c to C2/c.