Dielectric and direct temperature changes induced by an electric field were investigated in a ͗011͘-oriented 0.72Pb͑Mg 1/3 Nb 2/3 ͒O 3 -0.28PbTiO 3 single crystal as a function of temperature. Field-induced temperature changes were measured directly from the surface of the crystal by a thermocouple. Three distinct anomalies at temperatures of ϳ68, ϳ96, and ϳ128°C were identified in the dielectric and temperature change responses of the crystal, dividing the temperature range into four distinct phase stability regions with different field-induced behaviors. Just above the depolarization temperature of 128°C, dielectric hysteresis showed a double-loop nature caused by a reversible nonpolar-polar phase transition accompanied by an increase in the electrocaloric temperature change. Two other reversible field-induced phase transitions with different field-induced thermal behaviors were evidenced in the polarization and temperature responses in the temperature ranges of 96-128°C and below 68°C.

Transition metal dichalcogenides (TMDs) have received immense research interest in particular for their outstanding electrochemical and optoelectrical properties. Lately, chemical gas sensor applications of TMDs have been recognized as well owing to the low operating temperatures of devices, which is a great advantage over conventional metal oxide based sensors. In this work, we elaborate on the gas sensing properties of WS2 and MoS2 thin films made by simple and straightforward thermal sulfurization of sputter deposited metal films on silicon chips. The sensor response to H2, H2S, CO and NH3 analytes in air at 30 °C has been assessed and both MoS2 and WS2 were found to have an excellent selectivity to NH3 with a particularly high sensitivity of 0.10 ± 0.02 ppm−1 at sub-ppm concentrations in the case of WS2. The sensing behavior is explained on the bases of gas adsorption energies as well as carrier (hole) localization induced by the surface adsorbed moieties having reductive nature.

A perovskite solid-solution, (1-x)KNbO3-xBaNi1/2Nb1/2O3-δ (KBNNO), has been found to exhibit tunable bandgaps in the visible light energy range, making it suitable for light absorption and conversion applications, e.g., solar energy harvesting and light sensing. Such a common ABO3–type perovskite structure, most widely used for ferroelectrics and piezoelectrics, enables the same solid-solution material to be used for the simultaneous harvesting or sensing of solar, kinetic, and thermal energies. In this letter, the ferroelectric, pyroelectric, and piezoelectric properties of KBNNO with x = 0.1 have been reported above room temperature. The investigation has also identified the optimal bandgap for visible light absorption. The stoichiometric composition and also a composition with potassium deficiency have been investigated, where the latter has shown more balanced properties. As a result, a remanent polarization of 3.4 μC/cm2, a pyroelectric coefficient of 26 μC/m2 K, piezoelectric coefficients d33 ≈ 23 pC/N and g33 ≈ 4.1 × 10−3 Vm/N, and a direct bandgap of 1.48 eV have been measured for the KBNNO ceramics. These results are considered to be a significant improvement compared to those of other compositions (e.g., ZnO and AlN), which could be used for the same applications. The results pave the way for the development of hybrid energy harvesters/sensors, which can convert multiple energy sources into electrical energy simultaneously in the same material.

The electrocaloric effect (ECE) in the Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) solid solution system was investigated by means of detailed direct temperature measurements as a function of temperature, composition, and electric field. The (1−x)PMN-xPT ceramics of compositions 0 ≤ x ≤ 0.3 were fabricated by the columbite route. In opposite to conventional ferroelectrics, the maximum of electrocaloric effect was found to shift from the proximity of depolarization/Curie temperature to higher temperatures above a certain composition-dependent electric field strengths. Especially, the compositions with low PT content showed a broadened temperature range of electrocaloric effect. With increasing PbTiO3 concentration, the magnitude of ΔT increased, and the temperature dependence of the maximum ECE response gradually developed towards a more pronounced anomaly typical for conventional ferroelectrics. The arising high temperature electrocaloric effect in the ergodic relaxor phase was attributed to the contribution from polar nanoregions. All the compositions studied showed the highest electrocaloric activity just above the depolarization/Curie temperature close to the possible critical point, as recently predicted and observed for some compositions. The magnitude of the maximum electrocaloric temperature change was in the range of ΔT = 0.77–1.55 °C under an electric field strength of 50 kV/cm.

The electrocaloric effect in a 0.92Pb͑Zn 1/3 Nb 2/3 ͒O 3 -0.08PbTiO 3 single crystal was measured by a direct calorimetric technique as a function of sample temperature and electric field. The temperature of the maximum electrocaloric effect was found to coincide with the ferroelectric transition temperature. We present a theoretical description based on mean-field theory that gives a satisfactory description of the temperature and electric field dependence of the experimentally observed electrocaloric effect.

Modern environmental and sustainability issues as well as the growing demand for applications in the life sciences and medicine put special requirements to the chemical composition of many functional materials. To achieve desired performance within these requirements, innovative approaches are needed. In this work, we experimentally demonstrate that thermal strain can effectively tune the crystal structure and versatile properties of relatively thick films of environmentally friendly, biocompatible, and low-cost perovskite ferroelectric barium titanate. The strain arises during post-deposition cooling due to a mismatch between the thermal expansion coefficients of the films and the substrate materials. The strain-induced in-plane polarization enables excellent performance of bottom-to-top barium titanate capacitors akin to that of exemplary lead-containing relaxor ferroelectrics. Our work shows that controlling thermal strain can help tailor response functions in a straightforward manner.

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Ferroelectric phase inducing threshold electric field E th and its temperature dependence were determined in relaxor ferroelectric 0.87Pb͑Mg 1/3 Nb 2/3 ͒O 3 − 0.13PbTiO 3 ͑PMN-13PT͒ ceramics by measuring dielectric response on a dc field pulse. Evolution of the induced ferroelectricity was observed by means of polarization measurements. An inducing threshold field was found to have a minimum of E th,min = 1.55 kV/ cm at T = −5°C. In contrast to pure PMN, which shows a minimum threshold field near the depolarization temperature, the temperature of the minimum threshold field differs by an amount of ⌬T = 23°C from the depolarization temperature T dp =18°C in PMN-13PT. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2993345͔In prototype relaxor ferroelectrics Pb͑Mg 1/3 Nb 2/3 O͒ 3 ͑PMN͒, a ferroelectric long-range order can be made stable by adding pure ferroelectric PbTiO 3 ͑PT͒ to form a solid solution of Pb͑Mg 1/3 Nb 2/3 ͒ 1−x Ti x O 3 ͑PMN-xPT͒ 1 and by applying a dc electric field. 2,3 The structure of PMN exhibits average cubic symmetry down to very low temperatures. 4,5 On the other hand, a nanometer scale of 1:1 ordering of Mg 2+ and Nb 5+ cations leads to formation of polar nanoregions. 6 An increase in PT content gradually increases the degree of polar nanoregion evolution, thus favoring the development of a long-range polar order due to a reduced tendency of 1:1 ordering. 1 Eventually this leads to long-range dipolar correlation of the polar regions and onset of a ferroelectric rhombohedral phase. According to recent studies, however, ferroelectric distortion in low-temperature PMN-xPT ͑x Յ 0.2͒ appears to be limited to a short range in the bulk of a crystal with average cubic symmetry, and the polar regions of rhombohedral symmetry are present in a near-surface outer crystal. [7][8][9] This structural complexity makes it difficult to draw exact boundaries between adjacent phases, and it is believed to be a reason for the discovered contradiction in the PMN-PT structure. 9 Furthermore, the low-temperature ferroelectric structure develops into a tetragonal phase through intermediate monoclinic phases in the vicinity of the morphotropic phase boundary. 10,11 Thus, modification of PMN with PT enhances coupling of the polar nanoregions to the applied dc field and consequently decreases the threshold for field inducement.The electric field-induced ferroelectric transition and its temperature dependence on relaxor ferroelectrics are influenced by the type of transition enforcement. 12-14 Mostly heating and cooling with a constant electric field have been used to determine E-T relations of both PMN 14,15 and PMN-PT. 10,16 Nevertheless, another approach with constant temperature and a variable electric field requires a different kind of study in which field-inducing behavior can be viewed separately at individual temperatures.In this letter we study a field-induced ferroelectric transition in PMN-13PT ceramics. In particular, we examine the temperature dependence of the threshold field by measuring the die...