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In this work, the effects of thermal annealing at 500 {\deg}C on aerosol-deposited $0.65\text{Pb}(\text{Mg}_{1/3}\text{Nb}_{2/3})\text{O}_{3}-0.35\text{PbTiO}_{3}$ thick films on stainless-steel substrates are investigated using two complementary methods at high and low applied external electric fields. The first one is Positive Up Negative Down method, which allows us to obtain information about the switching and non-switching contributions to the polarization. It shows that the as-deposited film is ferroelectric before annealing, since it has a switching contribution to the polarization. After annealing, both the switching and non-switching contributions to polarization increased by a factor of 1.6 and 2.33, respectively, indicating stronger ferroelectric behavior. The second method is based on impedance spectroscopy coupled with Rayleigh analysis. The results show that post-deposition thermal annealing increases the reversible domain wall contribution to the dielectric permittivity by a factor 11 while keeping the threshold field similar. This indicates, after annealing, domain wall density is larger while domain wall mobility remains similar. These two complementary characterization methods show that annealing increases the ferroelectric behavior of the thick film by increasing the domain wall density and its influence is visible both on polarization versus electric field loop and dielectric permittivity.

Multiferroic CoFe2O4-Ba0.95Ca0.05Ti0.89Sn0.11O3 core-shell nanofibers (CFO@BCTSn NFs) were synthesized by a sol-gel co-axial electrospinning technique. The scanning electron microscope and transmission electron microscope were used to check nanofibers' core-shell structure/configuration. X-ray diffraction and a high-resolution transmission electron microscope were used to confirm the spinel structure of CFO and the perovskite structure of BCTSn. The magnetic character of the resultant CFO@BCTSn NFs was determined by SQUID magnetometry. The piezoelectricity was verified using piezo-response force microscopy, which revealed an entirely covered ferroelectric shell outline, in accordance with SEM and TEM observations. The magnetoelectric (ME) coefficient was measured as a function of the applied external DC magnetic field. The maximum ME coefficient obtained for the CFO@BCTSn NFs was 346 mV cm-1 Oe-1. The high magnetoelectric coupling suggests that CFO@BCTSn NFs could be a promising candidate for magnetic field sensor and magnetoelectric device applications.

Reliable and accurate characterization of the electrocaloric effect is necessary to understand the intrinsic properties of materials. To date, several methods have been developed to directly measure the electrocaloric effect. However, each of them has some limitations, making them less suitable for characterizing ceramic films, which rely almost exclusively on less accurate indirect methods. Here, a new approach is proposed to address the process of rapid heat dissipation in ceramic films and to detect the electrically induced temperature change before it thermally bonds with the surrounding elements. By using a polymer substrate that slows heat dissipation to the substrate and fast infrared imaging, a substantial part of the adiabatic electrocaloric effect in Pb(Mg1/3Nb2/3)O3-based ceramic films is captured. Infrared imaging provides a robust technique to reduce the ratio between the adiabatic and the measured electrocaloric temperature change in micrometer-sized ceramic films to a single-digit number, ~3.5. The obtained results are validated with another direct thermometric method and compared with the results obtained with an indirect approach. Despite different measurement principles, the results obtained with the two direct methods agree well. The proposed approach is timely and could open a door to verify the predicted giant electrocaloric effects in ceramic films, thus accelerating the process of their integration into functional devices.

The polarization and strain response of ferroelectric materials at fields below the macroscopic coercive field is of a paramount importance for the operation of many electronic devices. The response of real ferroelectric and related materials is in general complex and difficult to interpret. The reason for this is that many processes in a ferroelectric material contribute to its properties, often concurrently. Examples include motion of ferroelectric and ferroelastic domains, presence of domains within domains, dynamics of different types of polar nano-entities, interaction of polar nano-entities (e.g., polar nanoregions in relaxors) with the strain and polarization within domains, motion of defects and rearrangement of defect clusters and their interaction with polarization and strain. One signature of these processes is nonlinearity of the strain and polarization. Most ferroelectrics exhibit nonlinear response at all practical field levels meaning that the apparent material coefficients depend on the amplitude of the driving excitation. In this paper we show that an investigation of nonlinear behavior is a sensitive way to study various mechanisms operating in dielectric and piezoelectric materials. We review the basic formalism of the nonlinear description of polarization and strain, give a physical interpretation of different terms and illustrate this approach on numerous examples of relaxors, relaxor ferroelectrics, hard and soft ferroelectrics, and morphotropic phase boundary compositions. An experimental approach based on a lock-in technique that is well-suited for such studies is also discussed., Comment: main text 35 pages, 8 figures; supplementary material 3 pages and 5 figures

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano entities. The results question the existence of an ergodic state in PMN below Burns temperature., Comment: 14 pages main text, 5 pages supplementary information

The existence and feasibility of the multicaloric, polycrystalline material 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3, exhibiting magnetocaloric and electrocaloric properties, are demonstrated. Both the electrocaloric and magnetocaloric effects are observed over a broad temperature range below room temperature. The maximum magnetocaloric temperature change of ~0.26 K is obtained with a magnetic-field amplitude of 70 kOe at a temperature of 5 K, while the maximum electrocaloric temperature change of ~0.25 K is obtained with an electric-field amplitude of 60 kV/cm at a temperature of 180 K. The material allows a multicaloric cooling mode or a separate caloric-modes operation depending on the origin of the external field and the temperature at which the field is applied.

Elastic storage modulus and loss of relaxor lead magnesium niobate ceramics, Pb(Mg1/3Nb2/3)O3, have been measured with dynamic mechanical analyzer in single cantilever mode in the temperature range from 170 K to 320 K and at frequencies from 0.1 Hz to 50 Hz. The dependence of the elastic susceptibility (inverse modulus) on temperature and frequency of the driving force has characteristics of typical relaxor behavior that can be well described with the Vogel-Fulcher law. The parameters of the Vogel-Fulcher relation exhibit similar values for the dielectric and anelastic relaxations. Similarities and differences between anelastic and dielectric relaxor behaviors are identified., Comment: accepted in Applied Physics Letters