Electrocaloric effect in Ba(0.2)Ca(0.8)Ti(0.95)Ge(0.05)O(3) determined by a new pyroelectric method

The present letter explores the electrocaloric effect (ECE) in the lead free oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity (dT/dE) was determined by two different methods using the Maxwell relationship (dT/dE)~(dP/dT)_E. In a first well-known indirect method, P-E hysteresis loops were measured in a wide temperature range from which the pyroelectric coefficient p_E=(dP/dT)_E and thus (dT/dE) were determined by derivation of P(T,E) data. In the second novel method the pyroelectric coefficient p_E and consequently the electrocaloric responsivity was determined by direct measurements of the pyroelectric currents under different applied electric fields. Within the experimental error good agreement was obtained between two methods with an electrocaloric responsivity equal to 0.18 +/- 0.05 10-6 K.m.V-1 was obtained at about 410 KComment: 5 pages, 4 figure

Intrinsic dead layer effects in relaxed epitaxial BaTiO3 thin film grown by pulsed laser deposition

MEM acknowledges a support from the Region of Haut de France and IPR the Ministry of Education and Science of the Russian Federation (research project 3.1649.2017/PP).Epitaxial BaTiO3 (BT) thin film of about 400 nm thickness was grown on LaSr0.5Co0.5O3 (LSCO) coated (001)MgO using pulsed laser deposition. Ferroelectric properties of the BT thin film in Pt/BT/LSCO/MgO heterostructure capacitor configuration were investigated. Dynamic P-E hysteresis loops at room temperature showed ferroelectric behavior with Ps = 32 μC/cm2, Pr = 14 μC/cm2 and EC = 65 kV/cm. Static C-V measurements confirmed reversible switching with a coercive field EC = 15 kV/cm. Basing on a model taking into account an interface dead-layer we show that the capacitance-voltage “butterfly” loops imply only 25% switching of dipoles that inferred from dynamic polarization-field loops (~ 4 and ~ 16 kV/cm, respectively). Dielectric permittivity as a function of temperature revealed a first-order ferroelectric-to-paraelectric (FE-PE) phase transition in the BT film characterized by a maximum at TC ~ 130 °C. The very large (~ 126 K at 1 kHz) difference between TC and the extrapolated Curie-Weiss temperature T0 is attributed to the dead-layer effects.PostprintPeer reviewe

Structural investigation, dielectric, ferroelectric, and elecrocaloric properties of lead-free Ba(1-x)CaxTi(1-x)(Li1/3Nb2/3)(x)O3-delta (x=0.02 and x=0.07) ceramics

International audienceThe ferroelectric lead-free Ba(1-x)CaxTi(1-x)(Li1/3Nb2/3)(x)O3- with x=0.02 and x=0.07 (BCLNTO2 and BCLNTO7) ceramics were elaborated by a conventional sintering process. The effects of Ca and (Li, Nb) contents in the BTO matrix on the structure, dielectric, ferroelectric and electrocaloric properties were investigated. The refinement of the structure at room temperature showed that both BCLNTO2 and BCLNTO7 ceramics crystallize in the tetragonal system. Ferroelectric and dielectric investigations revealed the presence of three phase transitions similar to the parent phase BTO. Applying the Maxwell relation, the electrocaloric temperature changes were calculated using P-E hysteresis loops adjusted at different temperatures. The electrocaloric responsivity was found (max) (T/E)=0.14K mm/kV at T-ECmax = 374 and (max)=0.12K mm/kV at T-ECmax= 302K for BCLNTO2 and BCLNTO7, respectively

Reflow Soldering-Resistant Solid-State 3D Micro-Supercapacitors Based on Ionogel Electrolyte for Powering the Internet of Things

International audienceThe fabrication of all solid-state 3D micro-supercapacitor is challenging for powering connected and miniaturized emerging electronics devices in the frame of the future Internet of Things paradigm. Here we highlight the design of a specific solid electrolyte based on ethylmethylimidazolium bis(trifluoromethanesulfonate)imide confined within polyvinylidenefluoride which enables to meet the requirements of safety, easy packaging, and leakage free 3D micro-supercapacitors. This ionogel-based microdevice (2 mm × 2 mm footprint area) exhibits good cycling stability over 30 000 cycles with an areal energy density of 4.4 μWh.cm−2 and a power density of 3.8 mW.cm−2. It can also sustain the high temperature reflow soldering process (∼250 °C–5 min) without damage, which is performed to directly bond surface mounted miniaturized devices onto printed circuit boards. This strategy not only provides a reference for the design of high-performance 3D interdigitated micro-supercapacitors, but also paves the way to their further implementation in miniaturized electronic chips for Internet of Things applications

Indirect and direct electrocaloric measurements of (Ba1-xCax)(Zr0.1Ti0.9)O-3 ceramics (x=0.05, x=0.20)

International audienceElectrocaloric effect in lead-free (Ba1-xCax) (Zr0.1Ti0.9)O-3 ceramics (with x = 0.05 and x = 0.20) has been investigated by using two different indirect methods. In the first classic approach, the electrocaloric temperature change (Delta T) was calculated from the Maxwell relation based on measured P-E hysteresis loops recorded at different temperatures. In the second approach, the Delta T was calculated from the Maxwell relation based on pyroelectric current measurements. The advantage of such approach is that it enables direct determination of the pyroelectric coefficient, which should be otherwise calculated from the hysteresis loops in the classic approach. Direct method was finally used for verification of the obtained results. Good agreement between methods was found near the cubic-to-tetragonal phase transition temperature with a significant electrocaloric responsivity of Delta T/Delta E = 0.30 K mm/kV for the composition x = 0.05 obtained by direct method. (c) 2016 Elsevier B.V. All rights reserved

Impedance spectroscopy studies on lead free Ba 1-x Mg x (Ti 0.9 Zr 0.1 )O 3 ceramics

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Structural investigation, dielectric, ferroelectric, and elecrocaloric properties of lead-free Ba(1−x)CaxTi(1−x)(Li1/3Nb2/3)xO3−δ (x = 0.02 and x = 0.07) ceramics

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Structural, dielectric and electrocaloric properties in lead-free Zr-doped Ba0.8Ca0.2TiO3 solid solution

International audienceWe investigate in the present work the additional data points (x=0.02, 0.06 and 0.08) to the previous reported paper (Asbani et al., 2015) [21] that sufficiently enrich to understand the EC properties and underlying phase diagram of the lead-free Ba0.8Ca0.2Ti(1-x)ZrxO3 (xBCTZ) system. X-ray diffraction analysis performed at room temperature, confirms a continuous tetragonal solid solution with P4mm (No. 99) space group that evolved to pseudo-cubic symmetry for the high Zr-content compounds. Ferro electric and paraelectric behaviors were highlighted using P-E hysteresis data versus temperature. Phase transition was confirmed by dielectric permittivity measurements versus temperature showing a decrease of the Curie temperature when Zr-content increases. From P-E hysteresis recording the electrocaloric temperature change (Delta T) was calculated that ranged in between 0.12 and 0.27 K and the electrocaloric responsivity (xi) in 0.15 to 0.34 x 10(-6) K . m/V under 7.95 kV/cm applied electric field. The zero-field entropy is compared to electrocaloric isothermal entropy to estimate the extent the EC is being under-driven. (C) 2016 Elsevier Ltd. All rights reserved