Dielectric Relaxation Processes in Relaxor Ferroelectric Cd 2 Nb 2 O 7 Modified with Ni 2+ or Cu 2+

Abstract

The weak-field dielectric dispersion studies (100 Hz-13 MHz, 100 K < T < 300 K) of pyrochlore relaxor ferroelectric Cd 2 Nb 2 O 7 modified with Ni 2+ or Cu 2+ on the Cd 2+ site (at x = 0.02, 0.1, and 0.2) are presented and discussed. With increasing x, a relaxor behaviour of the system is manifested at higher temperature (around T C = 196 K and above). Around T C , the dielectric absorption spectra and relaxation-time distribution exhibit developing of two LF dielectric relaxation processes, in addition to ferroelectric domain wall motions: non-Debye relaxation typical of relaxors and Debye-like relaxation of quasi-isolated dipoles. The order parameter characterizing a deviation from Curie-Weiss dielectric behaviour in relaxors is nonzero up to ∼280 K, much higher than T C . The role of disorder on the Cd 2+ -site caused by randomly distributed off-center Ni or Cu ions (at x ≥ 0.1) is discussed.

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5OSmith1, Gardner2, Morrison3 et al. 2018Phys. Rev. Materials2020View full textAdd to dashboardCite

“…Shrout and Swartz show [88] that lead magnesium niobate also has a relaxor-like transition at a similar cryogenic temperature (T = 20K). The phase diagram in Cd2Nb2O7 is already known to be complicated [89][90][91][92][93][94][95][96][97][98], with seven phases, including an incommensurate one that locks in to monoclinic below T(lock-in) = 46K, and a glassy phase below Tg = 19K; but Pb2Nb2O7 has been more controversial. It is already known that mixed pyrochlores of formula (Cd,Pb)2(Nb,Ta)2O7 can be quantum ferroelectrics with Curie temperature Tc passing through zero.…”