Enhanced diffuse phase transition and defect mechanism of Na-doped Pb(Mg_1/3Nb_2/3)O₃ relaxor ferroelectrics

Abstract

The diffuse phase transition (DPT) characteristics and the associated defect mechanism of Na-doped Pb(Mg1/3Nb2/3)O3 (PMN) relaxor perovskite were studied. The enhanced DPT and the decrease in the intensity of the superlattice reflection were observed in the presence of Na2O. These contradictory observations were interpreted in terms of the inhibition of the growth of the 1 : 1 nonstoichiometric short-range ordered domains and the increase in the microcompositional fluctuation of the B-site cations caused by the formation of negatively charged Na′Mg sites. The mechanism of the associated defect process was then elucidated by analyzing the electrical conductivity as a function of the oxygen partial pressure. It was shown that the substitution of Na+ ions for Mg2+ ions in the B-site sublattice of perovskite PMN produced the negatively charged sites with a concomitant generation of oxygen vacancies () for the ionic compensation. This expedites the enhancement of the compositional inhomogeneities of the B-site cations and suppresses the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.

Calcium substituting B-site in relaxor ferroelectrics with perovskite structure probed by chemical ordering

“…Similarly, evidence of Na C substituting for Mg 2C in PMN has been recently reported by K.M. Lee et al when studied electrical conductivity as a function of oxygen partial pressure [24]. Thus it is quite possible that Ca 2C substitutes for B-site ions irrespective of the big size difference between Ca 2C and Bsite ions.…”

“…As well known, B-site ordered nanoregion with Mg:Nb raion of 1:1 carries a net negative charge with respect to the disordered matrix [7,23]. It is reported that acceptors (such as Na C ) could suppress B-site ordered region due to existence of Na 0 Pb with negative charge, which more enhances charge imbalance [7,24]. Thus, it is expected that substitution of Ca 2C on Nb 5C or Ti 4C could suppress B-site ordered region in the same way.…”

“…1, a deviation from the Curie-Weiss behavior is observed, which is typical character of relaxor ferroelectrics. Some investigations showed that the dielectric constant peak becomes much broader even though the degree of B-site order was increased [7,14,24]. Therefore, we could not elucidate the variation of B-site order by dielectric spectra.…”

Electrical properties and phase transition behaviors of Sr-doped 0.8PZT–0.2PNN ceramics

“…In complex lead-base perovskite such as PMN and PMN-PT (Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 ), many authors proposed that that 1:1 ordered nanoregion as observed by transmission electron microscope (TEM) is closely related to the degree of diffuse phase transition [14][15][16]. However, some authors proposed that the observation of diffuse phase transition can be related to the micro-composition fluctuation [17]. In the present work, it is believed that an increasing in degree of diffuseness of the phase transition may be attributed to the changes of nano-or micro-structure of the samples after doping.…”

A New Mechanism of Nonstoichiometric 1:1 Short‐Range Ordering in NiO‐Doped Pb(Mg1/3Nb2/3)O3 Relaxor Ferroelectrics

“…18 This contradictory observation was recently explained in terms of the substitution site for the added Na + ions. 21 It was shown that the added Na + ions did not act as acceptors in the A-site but rather substituted for Mg 2+ ions (or BЈ ions in Pb(BЈ 1/3 BЉ 2/3 )O 3 -type perovskites, in general) in the B-site sublattice of perovskite PMN. The partial substitution for the BЈ ions then promotes microcompositional inhomogeneity in the B-site sublattice, because of the increase in the types of B-site cations involved, which eventually enhances the extent of the DPT.…”