Structural phase transition and dielectric relaxation in Pb(Zn_1/3Nb_2/3)O₃single crystals

Abstract

The structure and the dielectric properties of Pb(Zn 1/3 Nb 2/3 )O 3 (PZN) crystal have been investigated by means of high-resolution synchrotron xray diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in the frequency range 100 Hz-1 MHz). At high temperatures, the PZN crystal exhibits a cubic symmetry and polar nanoregions inherent to relaxor ferroelectrics are present, as evidenced by the single (222) Bragg peak and by the noticeable tails at the base of the peak. At low temperatures, in addition to the well-known rhombohedral phase, another low-symmetry, probably monoclinic, phase is found. The two phases coexist in the form of mesoscopic domains. The ferroelectric phase transition is diffuse and observed between 325 and 390 K, where the concentration of the low-temperature phases gradually increases and the cubic phase disappears upon cooling. However, no dielectric anomalies can be detected in the temperature range of the diffuse phase transition. The temperature dependence of the dielectric constant shows a maximum at higher temperature (T m = 417-429 K, depending on frequency) with the typical relaxor dispersion at T < T m and the frequency dependence of T m fitted to the Vogel-Fulcher relation. Application of an electric field upon cooling from the cubic phase or poling the crystal in the ferroelectric phase gives rise to a sharp anomaly of the dielectric constant at T ≈ 390 K and greatly diminishes the dispersion at lower temperatures, but the dielectric relaxation process around T m remains qualitatively unchanged. The results are discussed in the framework of the present models of relaxors and in comparison with the prototypical relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 .

Thermal signatures of nanoscale inhomogeneities and ferroelectric order in[PbZn1/3Nb2/3Tachibana1, Sasame2, Kawaji3 et al. 2009Phys. Rev. B284440View full textAdd to dashboardCite

“…On the larger length scale, there is some controversy on the average structure of these systems. From conventional x-ray diffraction measurements, 29,30 it was believed that PZN shows a diffuse transition to the rhombohedral phase below 390 K, which is slightly lower than the peak temperature in the dielectric constant. On the other hand, high-energy x-ray diffraction studies 31 found no evidence of rhombohedral distortion down to much lower temperatures.…”

Phase Transition Near the Morphotropic Phase Boundary in Pb(Zn1/3Nb2/3)O3- PbTiO3

“…Recently, it was found that a sharp phase transition at 114 • C below the paraelectricferroelectric phase transition point appears in PZN under the conditions of the zero-field heating (ZFH) after a preceding field cooling (FC) [18][19][20][21], implying that decrease of heterogeneity owing to the applied electric field on the FC may make the phase transition sharp, which is usually smeared by the complex domain structures such as PNRs. The critical slowing down and temperature dependences of the second-and third-order nonlinear dielectric constants near this transition point were reported [22].…”

The interpretation and analysis of diffuse scattering using Monte Carlo simulation methods

“…Relaxor ferroelectrics have attracted tremendous attention in recent years because of their extraordinary dielectric and piezoelectric properties (Park & Shrout, 1997). Of these materials, the lead-based perovskite relaxor, Pb(Zn 1/3 Nb 2/3 )O 3 (PZN) has been one of the most extensively studied (Ye et al, 1999;Bing et al, 2005). Despite this, the exact nature of the structure and how it relates to its relaxor properties is still the subject of much controversy.…”