scholarly journals Theoretical Investigation of the Electrocaloric Properties of Lead-free Ferroelectric Ceramic

2020 ◽  
Author(s):  
Hend Kacem ◽  
Ahmad Dhahri ◽  
Mohamed Amara GDAIEM ◽  
Z. SASSI ◽  
L. SEVEYRAT ◽  
...  
Keyword(s):  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Entropy Change ◽  
Ferroelectric Ceramic ◽  
Solid State Reaction Method ◽  
Cooling Power ◽  
Promising Candidate ◽  
Theoretical Approaches ◽  
P4mm Space Group

Abstract BaTi0.91Sn0.09O3 (BST) sample was prepared by the solid-state reaction method. The structural, morphological and electrocaloric properties were studied. The sample crystallized in the tetragonal structure with P4mm space group. Based on mapping image, the sensitivity and spatial resolution of the different elements in our sample were improved. According to the variation of polarization as function of temperature, our sample had a paraelectric-ferroelectric phase transition, around room temperature. The electrocaloric properties of our sample were investigated using theoretical approaches. The important parameters such as maximum entropy change, relative cooling power and full width at half maximum were explained qualitatively. These results make our sample promising candidate for refrigeration domain.

Ferroelectricity of trimethylammonium bromide below room temperature

2020 ◽  
Vol 8 (17) ◽  
pp. 5868-5872 ◽  
Author(s):  
Zhangran Gao ◽  
Yuying Wu ◽  
Zheng Tang ◽  
Xiaofan Sun ◽  
Zixin Yang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
First Order

Ferroelectricity of trimethylammonium bromide was discovered near room temperature, which undergoes a first-order paraelectric–ferroelectric phase transition at the Curie temperature around 286 K.

scholarly journals Structural, magnetic and electrical properties of a new double-perovskite LaNaMnMoO 6 material

2017 ◽  
Vol 4 (11) ◽  
pp. 170920 ◽  
Author(s):  
Sameh Megdiche Borchani ◽  
Wissem Cheikh-Rouhou Koubaa ◽  
Makrem Megdiche
Keyword(s):  
Applied Field ◽  
Room Temperature ◽  
Double Perovskite ◽  
Entropy Change ◽  
Cooling Power ◽  
Room Temperature Resistivity ◽  
Ferromagnetic Transition ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
Xrd Patterns

Structural, magnetic, magnetocaloric, electrical and magnetoresistance properties of an LaNaMnMoO 6 powder sample have been investigated by X-ray diffraction (XRD), magnetic and electrical measurements. Our sample has been synthesized using the ceramic method. Rietveld refinements of the XRD patterns show that our sample is single phase and it crystallizes in the orthorhombic structure with Pnma space group. Magnetization versus temperature in a magnetic applied field of 0.05 T shows that our sample exhibits a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T C is found to be 320 K. Arrott plots show that all our double-perovskite oxides exhibit a second-order magnetic phase transition. From the measured magnetization data of an LaNaMnMoO 6 sample as a function of the magnetic applied field, the associated magnetic entropy change |−ΔSM| and the relative cooling power (RCP) have been determined. In the vicinity of T C , |−ΔSM| reached, in a magnetic applied field of 8 T, a maximum value of ∼4 J kg −1  K −1 . Our sample undergoes a large magnetocaloric effect at near-room temperature. Resistivity measurements reveal the presence of an insulating-metal transition at Tρ = 180 K. A magnetoresistance of 30% has been observed at room temperature for 6 T, significantly larger than that reported for the A 2 FeMoO 6 (A = Sr, Ba) double-perovskite system.

Ferroelectric Properties in Organic-inorganic Hybrid Material Tris(2-Hydroxyethyl) ammonium Trichloro Cadmium(Ⅱ)

2022 ◽  
Author(s):  
Zheng Tang ◽  
Xiaofan Sun ◽  
Zhangran Gao ◽  
Dong Li ◽  
Shulin Jiao ◽  
...  
Keyword(s):  
Phase Transition ◽  
Aqueous Solution ◽  
Hybrid Material ◽  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Ferroelectric Properties ◽  
Inorganic Hybrid ◽  
Space Group ◽  
Inorganic Hybrid Material

Organic-inorganic hybrid ferroelectric Tris(2-Hydroxyethyl) ammonium trichloro cadmium(Ⅱ) (TATC) with a space group of P21/c at room temperature was obtained in aqueous solution. There goes a paraelectric-ferroelectric phase transition (from monoclinic...

Origin of Ferroelectricity in Aurivillius Compounds

2000 ◽  
Vol 658 ◽  
Author(s):  
Donají Y. ◽  
Suárez Ian M. Reaney ◽  
William E. Lee
Keyword(s):  
Electron Microscopy ◽  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Tolerance Factor ◽  
Aurivillius Phases ◽  
Ferroelectric Phase Transition Temperature ◽  
Transmission Electron ◽  
Octahedral Tilting ◽  
Permittivity Measurements

ABSTRACTThe structures and microstructures of a range of Aurivillius phases have been investigated using transmission electron microscopy. Superlattice reflections arising from rotations of octahedra around the c-axis have been identified and their intensity at room temperature has been shown to diminish as the tolerance factor of the perovskite blocks increases. The paraelectric to ferroelectric phase transition temperature (Tc) has been monitored using permittivity measurements as a function of temperature and Tc has also been shown to decrease as tolerance factor increases. It is proposed that the onset of octahedral tilting and Tc are related in Aurivillius phases.

scholarly journals Valence Electron Distributions in Ferroelectric Barium Titanate Nanopowders

2014 ◽  
Vol 70 (a1) ◽  
pp. C746-C746
Author(s):  
Yoshihiro Kuroiwa ◽  
Masashi Yamada ◽  
Eisuke Magome ◽  
Chikako Moriyoshi ◽  
Hiroshi Tanaka ◽  
...  
Keyword(s):  
Phase Transition ◽  
Ferroelectric Phase Transition ◽  
Short Range ◽  
Room Temperature ◽  
Valence Electron ◽  
Ferroelectric Phase ◽  
Particle Sizes ◽  
Short Range Repulsion ◽  
Valence Electrons ◽  
Perovskite Type

Barium titanate BaTiO3 is one of the most important perovskite-type electroceramics, which undergoes the phase transition at 1300C from cubic to tetragonal, and exhibits ferroelectricity at room temperature. The phase transition depends on the particle size. BaTiO3 powders with the particle sizes less than several tens of nanometers are known to show no phase transition and hence no ferroelectricity at room temperature. The size effect of BaTiO3 is the most important issue in designing small ceramic capacitors with high capacitance. Our group has been devoted to visualizing the electron density distributions of perovskite-type oxides by analyzing the synchrotron-radiation x-ray powder diffraction (SXRD) data measured at SPring-8 using the maximum entropy method (MEM)/Rietveld method [1, 2]. In this study, the distributions of valence electrons in the outer shells of atoms are derived accurately from the SXRD data of BaTiO3 nanopowders to prove the characteristic chemical bondings which govern the ferroelectric phase transition. The powder samples used were 500 and 35 nm in particle sizes. The former showed the phase transition whereas the latter showed no phase transition. The MEM valence electron density studies at 2000C in the cubic structure revealed the clear structural variations that the Ti-O covalent bonding is found in the 500 nm sample, while all the valence electrons are localized at the O sites in the 35 nm sample exactly like an ionic crystal. Ferroelectricity originates from the balance between the long-rage Coulomb force and the short-range repulsion force. The obtained results provide direct experimental evidence that the electron orbitals hybridization on the Ti-O bonds weakens the short-range repulsion force, and causes the second-order Jahn-Teller distortion on the TiO6 octahedron in the 500 nm sample. We consider that the Ti-O bonding in the prototype structure governs the ferroelectric phase transition temperature in BaTiO3.

Tailoring the Magnetic Properties and Magnetocaloric Effect in Double Perovskites Sr2FeMo1–xNbxO6

2020 ◽  
Vol 12 (3) ◽  
pp. 391-397 ◽  
Author(s):  
Imad Hussain ◽  
S. N. Khan ◽  
Tentu Nageswara Rao ◽  
Riyaz Uddin ◽  
Jong Woo Kim ◽  
...  
Keyword(s):  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Double Perovskite ◽  
Entropy Change ◽  
Solid State Reaction Method ◽  
Cooling Power ◽  
X Ray Diffraction ◽  
Site Disorder ◽  
Magnetocaloric Properties ◽  
Arrott Plots

The crystal structure, magnetic and magnetocaloric properties of the Sr2FeMo1–xNbxO6 (0 ≤ x ≤ 0.3) samples prepared by solid state reaction method were investigated using X-ray diffraction (XRD) and magnetic measurements. The room temperature XRD profiles obtained for all the samples revealed the formation of the double perovskite tetragonal structure with I4/mmm symmetry. Maximum values of spontaneous magnetization (17.6 emu/g at 150 K) and Curie temperature, TC (380 K) were observed in the Sr2FeMo0.9Nb0.1O6 sample indicating that low Niobium (Nb) substitution (x = 0.1) at the Mo site in the host material resulted in higher magnetization and TC. Lower values of magnetization and TC were recorded in the samples with higher Nb concentration (x = 0.2, 0.3) that was attributed to the decrease in orbital hybridization and increase in anti-site disorder resulting from heavy doping. A second order of the magnetic phase transition in each sample was confirmed by the magnetization measurements and Arrott plots. The maximum magnetic entropy change and relative cooling power (RCP) were enhanced in lowest Nb doped sample (x = 0.1) suggesting that this compound can be used in magnetic refrigeration technology.

Iron Oxide-based Magnetic Nanoparticles for High Temperature Span Magnetocaloric Applications

2014 ◽  
Vol 1708 ◽  
Author(s):  
V. Chaudhary ◽  
R. V. Ramanujan
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Magnetic Nanoparticles ◽  
Room Temperature ◽  
Magnetic Entropy Change ◽  
Average Crystallite Size ◽  
Entropy Change ◽  
Superparamagnetic Nanoparticles ◽  
Cooling Power ◽  
Magnetic Entropy

ABSTRACTThe magnetocaloric effect of chemically synthesized Mn0.3Zn0.7Fe2O4 superparamagnetic nanoparticles with average crystallite size of 11 nm is reported. The magnitude of the magnetic entropy change (ΔSM), calculated from magnetization isotherms in the temperature range of 30 K to 400 K, increases from - 0.16 J-kg-1K-1 for a field of 1 T to - 0.88 J-kg-1K-1 for 5 T at room temperature. Our results indicate that ΔSM values are much higher than primarily reported values for this class of nanoparticles. ΔSM is not limited to the ferromagnetic-paramagnetic transition temperature; instead, it occurs over a broad range of temperatures, resulting in high relative cooling power.

Performance Assessment and Layer Fraction Optimization of Gd–Y Multilayer Regenerators for Near Room-Temperature Magnetic Cooling

2020 ◽  
Vol 28 (03) ◽  
pp. 2050027 ◽  
Author(s):  
Henrique N. Bez ◽  
Alan T.D. Nakashima ◽  
Gusttav B. Lang ◽  
Bruno S. de Lima ◽  
Antonio J.S. Machado ◽  
...  
Keyword(s):  
Figure Of Merit ◽  
Room Temperature ◽  
Entropy Change ◽  
Cooling Power ◽  
Reasonable Accuracy ◽  
One Dimensional ◽  
Magnetic Cooling ◽  
Refrigerant Capacity ◽  
Adiabatic Temperature Change ◽  
Numerical Assessment

An experimental and numerical assessment of multilayer active magnetic regenerators (AMR) composed of gadolinium (Gd) and gadolinium–yttrium (Gd–Y) alloys (Gd[Formula: see text]Y[Formula: see text], Gd[Formula: see text]Y[Formula: see text] and Gd[Formula: see text]Y[Formula: see text]) is presented. First, by calculating the adiabatic temperature change and the isothermal entropy change from the experimental data for the above materials, we show that, with reasonable accuracy for engineering design purposes, these properties can be determined by shifting the properties of pure Gd to the Curie temperature of the Gd–Y alloy — a common but not yet validated assumption in the design of Gd–Y AMRs with a low Y content. Next, we show that the optimal Gd–Y layer fraction in multilayer AMRs can be determined using the figure of merit known as the material refrigerant capacity (RC), which agrees well with the results from a more complex one-dimensional thermal non-equilibrium porous medium AMR model. Finally, the performance of the latter model is verified against the experimental cooling power data for two- and three-layer Gd–Y regenerators at temperature spans of 25, 30 and 35[Formula: see text]K.

scholarly journals Up-conversion luminescence of Er3+ and Yb3+ co-doped CaBi2Ta2O9 multifunctional ferroelectrics

2014 ◽  
Vol 04 (03) ◽  
pp. 1450018 ◽  
Author(s):  
Qiufeng Cao ◽  
Dengfeng Peng ◽  
Hua Zou ◽  
Jun Li ◽  
Xusheng Wang ◽  
...  
Keyword(s):  
Room Temperature ◽  
Ferroelectric Properties ◽  
Green Emission ◽  
Solid State Reaction Method ◽  
Fluorescence Intensity Ratio ◽  
Promising Candidate ◽  
Radiative Relaxation ◽  
High Temperature Sensor ◽  
Simple Solid State Reaction ◽  
Co Doped

Er 3+ and Yb 3+ co-doped CaBi 2 Ta 2 O 9 (CBT)-based bismuth layered-structure oxides were synthesized by a simple solid-state reaction method. Their up-conversion (UC) luminescence, dielectric and ferroelectric properties were investigated. Two strong green emission bands centered at 526 and 547 nm and a weak red emission band centered at 658 nm were obtained under a 980 nm laser excitation at room temperature. These emission bands originated from the radiative relaxation of Er 3+ from 2 H 11/2, 4 S 3/2, and 4 F 9/2 levels to the ground state 4 I 15/2, respectively. At the meantime, the fluorescence intensity ratio (FIR) variation of two green UC emissions at 526 and 547 nm has been studied as a function of temperature in the range of 153–603 K. The maximum sensor sensitivity obtained was 39 × 10-4 K-1 at 590 K, which indicated that Er 3+/ Yb 3+ co-doped CBT ceramic is a promising candidate for applications in optical high temperature sensor.

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