Ismail kriaa - Academia.edu (original) (raw)
Papers by Ismail kriaa
Journal of Electronic Materials, 2015
Electrocaloric (EC) cooling based on the ability of materials to change temperature by applying a... more Electrocaloric (EC) cooling based on the ability of materials to change temperature by applying an electric field under adiabatic conditions is a relatively new and challenging direction in ferroelectrics research. Analytical and simulation data for the electrocaloric effect (ECE) in 0.75Pb(Mg 1/3 Nb 2/3)O 3-0.25PbTiO 3 (0.75PMN-0.25PT) bulk ceramic samples are reported. The adiabatic temperature change (DT) due to a change of the external electric field has been calculated indirectly from the entropy change. The temperature change increases with an increase in the applied electric field and reaches a maximum of 2.1 K in 25 kV/cm electric field shift near the Curie temperature of 398 K; that is, the cooling DT per unit field (MV/m) is 0.896 9 10 À6 m K/V. This value is significantly large for bulk ceramics and makes the compound promising for room-temperature electric cooling applications.
Journal of Alloys and Compounds
Abstract The magnetic, magnetocaloric and critical behavior properties of 0.8BiFeO3-0.2BaTi0.95(Y... more Abstract The magnetic, magnetocaloric and critical behavior properties of 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroic ceramic are studied around its magnetic transition temperature: TC. The Rietveld Refinement of X-ray diffraction data, recorded at room temperature, revealed that our sample crystallizes in the tetragonal P4mm space group. The dependence of magnetization on temperature reveals a magnetic transition at TC = 365 K, which was confirmed via in-situ Mossbauer measurements. Around the magnetic transition temperature TC, the magnetic entropy change reached maximum value of Δ S M M a x of 10.0066 J. kg−1 K−1 and the relative cooling power (RCP) value is of 278.4014 J. kg−1, when a magnetic field of 5T is applied. The critical exponents β, γ and δ have been deduced via various methods: the modified Arrott plots (MAP), Kouvel-Fisher method (KF) and critical isotherm (CI) analysis. These critical exponent values confirm that δ values is between the mean-field model and the 3D-Heisenberg model, the β value is so close to the 3D-Heisenberg model while that γ value is proximate to the mean-field model. These critical parameters associated with the critical magnetic transition region predict the presence of both short and long magnetic range order in our sample. The precision of the deduced critical exponents is highlighted through the follow-up of the dependence of magnetization on temperature and magnetic field to the scaling theory. All the obtained results confirm the coexistence of the effect of two networks in our ceramics, the ferromagnetic ordering spin contribution, resulting in modulating the antiferromagnetic AFM canted spin, and the AFM ones, with both contributions of short- and long-range interactions, respectively, embedded in the spin glass like matrix BiFeO3. A number of attractive features made our 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroics as a potential candidate in a large area of modern applications.
Journal of Electronic Materials, 2015
Electrocaloric (EC) cooling based on the ability of materials to change temperature by applying a... more Electrocaloric (EC) cooling based on the ability of materials to change temperature by applying an electric field under adiabatic conditions is a relatively new and challenging direction in ferroelectrics research. Analytical and simulation data for the electrocaloric effect (ECE) in 0.75Pb(Mg 1/3 Nb 2/3)O 3-0.25PbTiO 3 (0.75PMN-0.25PT) bulk ceramic samples are reported. The adiabatic temperature change (DT) due to a change of the external electric field has been calculated indirectly from the entropy change. The temperature change increases with an increase in the applied electric field and reaches a maximum of 2.1 K in 25 kV/cm electric field shift near the Curie temperature of 398 K; that is, the cooling DT per unit field (MV/m) is 0.896 9 10 À6 m K/V. This value is significantly large for bulk ceramics and makes the compound promising for room-temperature electric cooling applications.
Journal of Alloys and Compounds
Abstract The magnetic, magnetocaloric and critical behavior properties of 0.8BiFeO3-0.2BaTi0.95(Y... more Abstract The magnetic, magnetocaloric and critical behavior properties of 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroic ceramic are studied around its magnetic transition temperature: TC. The Rietveld Refinement of X-ray diffraction data, recorded at room temperature, revealed that our sample crystallizes in the tetragonal P4mm space group. The dependence of magnetization on temperature reveals a magnetic transition at TC = 365 K, which was confirmed via in-situ Mossbauer measurements. Around the magnetic transition temperature TC, the magnetic entropy change reached maximum value of Δ S M M a x of 10.0066 J. kg−1 K−1 and the relative cooling power (RCP) value is of 278.4014 J. kg−1, when a magnetic field of 5T is applied. The critical exponents β, γ and δ have been deduced via various methods: the modified Arrott plots (MAP), Kouvel-Fisher method (KF) and critical isotherm (CI) analysis. These critical exponent values confirm that δ values is between the mean-field model and the 3D-Heisenberg model, the β value is so close to the 3D-Heisenberg model while that γ value is proximate to the mean-field model. These critical parameters associated with the critical magnetic transition region predict the presence of both short and long magnetic range order in our sample. The precision of the deduced critical exponents is highlighted through the follow-up of the dependence of magnetization on temperature and magnetic field to the scaling theory. All the obtained results confirm the coexistence of the effect of two networks in our ceramics, the ferromagnetic ordering spin contribution, resulting in modulating the antiferromagnetic AFM canted spin, and the AFM ones, with both contributions of short- and long-range interactions, respectively, embedded in the spin glass like matrix BiFeO3. A number of attractive features made our 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroics as a potential candidate in a large area of modern applications.