Phase transition in nasicon (Na3Zr2Si2PO12)

A second order phase transition has been found in Na3Zr2Si2PO12 by three independent techniques i. Electrochemical investigations including ac-impedance technique showed a reversible change in the activation energy for Na-ion conduction from 34.2 kJ mol−1 at temperatures below 425 K to 20 kJ mol−1 for higher temperatures. ii. Specific heat measurements show a clear indication of a phase transition at 420 K with ΔH = 2.07 kJ mol−1. iii. High temperature X-ray diffraction powder patterns reveal a change from the monoclinic into the rhombohedral phase at the transition point.