Relaxor–ferroelectric crossover seen via characteristic temperatures of Ba_xSr_1–xTiO₃ ferroelectrics detected by acoustic emission

Abstract

BaxSr1–xTiO3 ferroelectrics ceramic with x = 70 and 80% have been studied by means of acoustic emission over a wide 0–300 °C temperature range and under dc external electric field. All the Curie temperatures Tc, intermediate temperatures T*, and Burns temperatures Td have been successfully detected and compared with those previously detected in BaxSr1–xTiO3 with x = 60% and pure BaTiO3, using the acoustic emission. For all the compounds, the critical end points at which the strains are expected to be largest, have been successfully detected, too. While the Tc linearly increases as x increases, it was established that both the T* and Td exhibit nonlinear behavior: they initially decrease, attain the minima near x ≈ 70% and then start to increase and tend to those, corresponding to pure BaTiO3, as it was previously reconstructed for Td in BaZrxTi1–xO3 compound [Shvartsman and Lupascu, J. Am. Ceram. Soc. 95, 1 (2012)]. Such a phenomenon is discussed from the viewpoint of the presence of polar nanoregions, intrinsic to pure BaTiO3 in the paraelectric phase, and it is concluded, that a minimum in both the T*(x) and Td(x) dependences points out a range of relaxor–ferroelectric crossovers in Ba‐based compounds.

Electric field dependences of Curie and Néel phase transition temperatures in magnetoelectric relaxor multiferroic Pb(Fe0.5 Ta0.5 )O3 crystals seen via acoustic emission

“…Figure shows behavior of T N and corresponding in dependence on dc electric field E . T N linearly decreases and corresponding decreases monotonically, too, as E enhances, similar that the decreases after attaining a maximum in the critical point . Such influence of electric field on T N points to strong magnetoelectric coupling in PFT.…”

“…T c 1 ( E ) exhibits a nonlinear behavior, characteristic for RFEs : it initially decreases, attains a sharp minimum at T th 1 ≈ 247 K and at the threshold field E th ≈ 0.1 kV cm −1 , and then starts to increases, as E enhances, similar to ordered FEs. This order of magnitude of E th is in a good agreement with the previous obtained data in some REFs , but in a contradiction with the E th ≈ 3 kV cm −1 in Li‐doped PFT ceramics . We speculate that such a large value of the latter data is caused by doping of Li in PFT to increase a resistance of the samples.…”

“…_ N c1 of AE increases monotonically without any maximum, corresponding to an end critical point [6,10,62], recently found in RFEs by maximum in heat capacity [63], and pyroelectric coefficient [64,65]. It is noteworthy that a pyroelectric coefficient of Li doped PFT ceramics exhibits no maximum, corresponding to an end critical point too, but tends to saturation [46].…”

“…Both Pb‐based and Pb‐free A(B′ 1/2 B″ 1/2 )O 3 and A(B′ 1/3 B″ 2/3 )O 3 RFEs attract a great attention due to their intrinsic chemical inhomogeneity and related local structural distortions due to the difference in ionic charges and radii between the different kinds of B‐site cations in the former , as well as either on A‐ or B‐ or on both A‐ and B‐sites in the latter . The spatial variations in these cation distribution result in an overall chemically disordered host matrix, possessing local electric fields (often called random fields, RFs) , and chemically short‐range ordered regions with the size of about 5–15 unit cells of the aristotype structure , giving rise to polar nanoregions (PNRs), resembling the FE domains (dipoles), possessing a spontaneous polarization, and dispersed within a cubic nonpolar paraelectric phase (PE) , responsible for the outstanding properties of the RFEs, such as: (i) giant and smeared maxima of dielectric permittivity ( ɛ ), a temperature maximum, T m , of which depends on the measuring frequency , and (ii) nonlinear behavior of this T m in dependence on external dc electric field –so‐called V‐shape .…”

“…So, all the points, characteristic for RFEs, as well as all the phase transitions, characteristic of ferroelectric multiferroics, were successfully detected. Figure 2 shows behavior of T c1 and corresponding _ N c1 , determined from AE, in dependence on dc electric field E. T c1 (E) exhibits a nonlinear behavior, characteristic for RFEs [5][6][7][8][9][10][11]: it initially decreases, attains a sharp minimum at T th1 % 247 K and at the threshold field E th % 0.1 kV cm À1 , and then starts to increases, as E enhances, similar to ordered FEs. This order of magnitude of E th is in a good agreement with the previous obtained data in some REFs [5][6][7][8][9][10][11], but in a contradiction with the E th % 3 kV cm À1 in Li-doped PFT ceramics [46].…”