Successful aqueous processing of a lead free 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 piezoelectric material composition

We report on the successful aqueous processing of a lead free piezoelectric 0.5Ba(Zr0.2Ti0.8)O-3-0.5( Ba0.7Ca0.3)TiO3 (BZT-BCT) composition with the final functional properties of the materials unaffected by the various processing steps involved. X-ray diffraction results show a single tetragonal perovskite crystalline phase for the as-received sintered BZT-BCT powder. The purity of the perovskite phase for BZT-BCT powder was found to be controlled even after ageing the material in water for 24 h as a successful surface treatment against hydrolysis. An aqueous suspension of surface treated BZT-BCT powder with 50 vol% solid loading was successfully transformed into micro-sized granules via a freeze granulation (FG) method. Various structural, electrical and mechanical properties of sintered BZT-BCT-FG and BZT-BCT-NG ceramics consolidated from freeze granulated and non-granulated (NG) powders, respectively, were measured. The dielectric constant (epsilon(r)) values of the BZT-BCT-FG sample were found to be higher, with lower dielectric loss (tan delta) values in comparison with those of a sample prepared from the BZT-BCT-NG powder at all temperatures and with all frequency ranges tested. Nanoindentation results revealed that the ability to oppose deformation was nearly 10-fold higher for BZT-BCT-FG (6.93 GPa) than for BZT-BCT-NG ceramics (543 MPa). The functional properties of BZT-BCT- FG samples confirmed the benefits of the aqueous processing approach in comparison with traditional dry pressing

Numerical simulation of heat conduction for the growth of anisotropic layered GaSe crystals

WOS: 000223853900005In this report, we present the usage of a second rank cylindrical conductivity tensor which we derived to simulate the crystal growth processes of a layered compound GaSe in a cylindrical enclosure by directional solidification. Use of such a tenser is inevitable in the simulations of the growth of highly anisotropic crystals having layered structure, since the crystallographic orientation of the grown material is not necessarily aligned with the ampoule symmetry. Using the finite difference control volume approach in 3D, we solved transient heat conduction equation for a highly anisotropic solid in a cylindrical enclosure. We obtained sloped thermal fields and isothermal surfaces and the magnitudes of the slopes are strong functions of both azimuthal angle and growth orientation. The results showed that the orientation of the crystallographic axes of GaSe in the enclosure is quite effective in the steady and the transient fields, isotherms, and axial and radial temperature gradient within the material. Increase of Bi number decreases the magnitude of the slope of isothermal surface. Anisotropy of the conductivity seems to be effective in the orientation of the growth direction of the resulting crystal within the cylindrical ampoule

The Structural, Magnetic, and Magnetocaloric Properties of La1-x Ag (x) MnO (3) (0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.25)

WOS: 000379347200018We have investigated structural, magnetic, and magnetocaloric properties of monovalent Ag-doped La1-x Ag (x) MnO3 (0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.25) compounds. The materials were prepared by the sol-gel method and then characterized by X-ray diffraction (XRD). The XRD results indicated that all the samples have a single phase of hexagonal (rhombohedral) structure with the space group. The morphology and particle size distributions were investigated using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The SEM images showed that the grain sizes are smaller than 1 mu m and remain the same with increasing Ag concentrations. The magnetic properties were studied by measuring magnetization and varying temperature (M(T)) and external magnetic field (M(H)). The M(T) measurements show that with decreasing temperature all samples exhibit a paramagnetic-to-ferromagnetic phase transition. The Curie temperature, T (C), increases from 200 to 290 K as Ag doping increases from 0.05 to 0.25. The magnetic entropy change (|-SM|) is obtained in all samples near the Curie temperatures at a magnetic field change of 3 T. Furthermore, their maximum relative cooling power (RCP) values were found to be 82.492, 82.614, and 127.375 J/kg for x = 0.10, 0.15, and 0.25

Structural, Electrical, and Magnetic Properties of High-Temperature-Sintered La1-xNaxMnO3 (0.05 <= x <= 0.35) Compounds

WOS: 000346703800043The structural, electric, and magnetic properties of La1-xNaxMnO3 (0.05 <= x <= 0.35) compounds have been investigated. The compounds were prepared by a standard sol-gel method then sintered at 1400 degrees C for 24 h. The crystal structures were orthorhombic (Pbnm) for all Na concentrations, and the unit cell volumes, determined from the x-ray diffraction data, tended to decrease with increasing Na content. The high-temperature-sintering process resulted in a grainy structure with grain sizes of 5-30 mu m. The Curie temperature (T-C) increased with increasing Na concentration up to x = 0.20, then decreased with further increase in Na concentration. The maximum magnetic entropy change (-Delta S-M) under a field change of 1.6 T was calculated to be similar to 3 J/kg K for the sample containing 15% Na

The influence of the sintering temperature on the structural and the magnetic properties of doped manganites: La0.95Ag0.05MnO3 and La0.75Ag0.25MnO3

Unlu, C. Gokhan/0000-0003-2554-5886; IRMAK, Ali Ekber/0000-0003-4047-7869; Kaynar, Mehmet Burak/0000-0002-4854-8142WOS: 000274232300010La1-xAgxMnO3 samples were synthesized by standard sol-gel method with Ag concentrations of x = 0.05 and 0.25. The samples from each concentration were pressed and sintered at 1000, 1200 and 1400 degrees C for 24 h in air for a systematic study. They were examined structurally by Atomic Force Microscopy (AFM), Scanning Electron Microscopy(SEM) with Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) and magnetically by Magnetic Properties Measurements System (MPMS). AFM and SEM analyses show that surface morphology changes with Ag concentration and sintering temperature (T-S). It was observed that high temperature sintering leads Ag to leave material as determined from EDS analyses. XRD spectra exhibited that the crystal structure changes with Ag concentration while showing pronounced change with the sintering temperature. From the magnetic measurements, the Curie temperatures (T-C) and the isothermal magnetic entropy changes (-Delta SM) were calculated. It was observed that T-C increases with Ag concentration and decreases with T-S. The maximum -Delta SM was calculated to be 7.2 J/kg K under the field change of 5 T for the sample sintered at 1000 degrees C with x = 0.25. (C) 2009 Elsevier B.V. All rights reserved

Effect of high temperature sintering on the structural and the magnetic properties of La1.4Ca1.6Mn2O7

Unlu, C. Gokhan/0000-0003-2554-5886; Aksoy, Seda/0000-0002-7823-7070; IRMAK, Ali Ekber/0000-0003-4047-7869; Sarikurkcu, Cengiz/0000-0001-5094-2520WOS: 000287968000004We investigate the effect of sintering temperature on the structural and magnetic properties of La1.4Ca1.6Mn2O7 double perovskite manganite compound prepared by the sol-gel route. Three sintering temperatures (1273, 1473 and 1673 K) are utilized for the heat treatment. Regardless of the sintering temperature, the tetragonal crystal structure with the I4/mmm space group is stable. However, a reduction in a and an increase in c lattice parameters along with a significant increase in crystallite-size occur on increasing the sintering temperature. This is also accompanied by the growth of grains. Grain-growth and changing crystallite-sizes account for the changes in magnetization, Curie temperature and magnetic entropy-change values. As the sintering temperature increases from 1273 to 1673 K the Curie temperature increases from 225 to 268 K and the magnetic entropy-change increases from 0.58 to 3.1 J kg(-1) K-1 respectively. (C) 2010 Elsevier B.V. All rights reserved.Erasmus Mobility ProgrammeThe authors would like to acknowledge Erasmus Mobility Programme for supporting Gokhan Unlu and Yusuf Samancoglu at Experimentalphysik AG Farle Laboratory at Duisburg-Essen University

What do we need for the lithium-air batteries: A promoter or a catalyst?

LaSr-based perovskite materials are frequently studied as catalyst at the cathode of the lithium-air batteries (LAB). In this study, we compared Pb, Ba and Sr in the form of La0.65X0.35MnO3 (X = Pb, Ba, Sr) at the cathode of LAB in terms of total discharge capacity, cell cycling and discharge reaction products. The electrochemical characterization was carried out at the discharge current density of 200 mA g−1 under dry oxygen atmosphere. The cell with La0.65Pb0.35MnO3, La0.65Ba0.35MnO3 La0.65Sr0.35MnO3 and Acetylene black carbon (alone) displayed capacity values of 7211 mAh g−1, 6205 mAh g−1, 6760 mAh g−1 and 5925 mAh g−1, respectively. The number of cycle and the operation time with the cells using La0.65Pb0.35MnO3, La0.65Ba0.35MnO3, La0.65Sr0.35MnO3 and Acetylene black carbon (alone) at 0.1 mA cm−2 were 35 (650 h), 18 (300 h), 20 (76 h) and 11 (64 h), respectively. The cells with La0.65Pb0.35MnO3 showed columbic efficiencies ranging from 95 to 97% with superior performance compared to La0.65Ba0.35MnO3 and La0.65Sr0.35MnO3 with columbic efficiency of about 87%. The overpotential value was decreased approximately 300 mV by the use of La0.65Sr0.35MnO3 as a catalyst, whereas no change in the overpotential value was observed by the use of La0.65Ba0.35MnO3 and La0.65Pb0.35MnO3 as a promote

Magnetic properties of La0.65Ca0.30Pb0.05Mn0.9B0.1O3 (B = Co, Ni, Cu and Zn)

WOS: 000345749500123The La0.65Ca0.30Pb0.05Mn0.9B0.1O3 (A = Co, Ni, Cu and Zn) manganites have been prepared via sol-gel method and sintered at 1100 degrees C for 24 h. The aim of the study was to investigate B-site cation doping effects on the magnetic properties. XRD analysis reveals that all samples have rhombohedral structure belonging to the R (3) over barc space group. The Curie temperature decreases as a result of Mn replacement with Co, Ni, Cu and Zn, respectively. The maximum magnetic entropy changes of the samples doped with Co, Ni, Cu and Zn for a field change of 1 T were found to be 2.10, 1.71, 3.20 and 1.42 J/kg K respectively. For La0.65Ca0.30Pb0.05MnO3, this is 2.60 J/kg K. The maximum magnetic entropy change increases as a result of Cu doping. Additionally, the metal-insulator transition temperature decreases due to the B-site doping. (C) 2014 Elsevier B.V. All rights reserved