Synthesis and characterization of multiferroic magnetoelectric ceramic composites

Ceramic composites with composition (1−x)[Ba0.85Ca0.15Zr0.1Ti0.9O3] − x[Ni0.7Zn0.3Fe2O4], (0 ≤ x ≤ 100 wt%) were prepared using solid state route. Structural and microstructural analysis confirmed the coexistence of ferroelectric (BCZT) and magnetostrictive (NZFO) phases without any detectable presence of impurity/secondary phases. The composites exhibited ferroelectric, magnetic properties and magnetoelectric coupling responses. Highest coupling coefficient was obtained for composite with 50 wt% NZFO.publishe

Low temperature magnetic and magnetocaloric studies in YCr0.85Mn0.15O3 ceramic

We have investigated low temperature magnetic and magnetocaloric properties of manganese (Mn) doped YCr0.85Mn0.15O3 (YCMO) polycrystalline compound, synthesized via solid state reaction route. The lattice volume was found to increase in comparison to that of pristine YCrO3 (YCO) compound. On the other hand, the paramagnetic-antiferromagnetic Néel temperature (TN ∼ 132 K) was found to be lower than that for YCO ceramic. On cooling below TN, under field cooled (FC) mode with an applied magnetic field of 0.02 T, magnetization flipped the polarity from positive to negative at Tcomp = 62 K. Furthermore, the magnetization switching temperature, defined as compensation temperature, exhibited field dependency and decreased with increasing field. Besides, the magnetization reversal phenomenon disappeared under higher applied magnetic field values. For the first time, the magnetocaloric effect for this compound was measured near 36 K through the parameters like magnetic entropy change (−ΔS) = ∼0.186 J kg−1 K−1 and the relative cooling power (RCP) ∼ 6.65 J kg−1, under an applied field of 5 T.publishe

Structural, electrical, optical and magnetic properties of SmCrO3 chromites: influence of Gd and Mn co-doping

Impact of co-doping of Gadolinium (Gd) and Manganese (Mn) ions on the structural, electrical, optical and magnetic properties of SmCrO3 (SCO) orthochromite compound has been systematically investigated for the first time. The lattice volume expanded with only Mn substitution whereas it shrinks in the co-doped compounds. The tolerance factor decreased while the orthorhombic distortion was found to increase with co-doping. Tilt angle, θ[101] (ο) increased in the co-doped compounds. On the contrary, ∅[010] (ο) initially decreased and then increased. The increased orthorhombic distortion with co-doping also influenced the Raman modes. The electrical resistivity got enhanced in the co-doped samples and its behavior was explained based on Mott's variable range hopping model. Hopping energy and mean hopping distance have also been estimated for the co-doped compounds. The optical bandgap of pristine SCO compound was observed to vary with co-doping, signifying the potential applications of these compounds as photocatalyst. Two compensation temperatures (defined as a temperature where the magnetization changes polarity) were noticed in co-doped compounds. The magnetization reversal was observed in all the co-doped compounds under lower applied magnetic field. The low temperature magnetocaloric effect got enhanced significantly with increasing co-doping content implying the usefulness of these compounds as low temperature refrigerant materials.publishe

Synthesis and characterization of lead-free 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 ceramic

Polycrystalline sample of lead-free 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 ceramic has been synthesized by solid state reaction method. Single-phase perovskite structure with rhombohedral symmetry was confirmed by x-ray diffraction. Temperature dependent dielectric permittivity studies demonstrated frequency independent behavior, indicating that the studied sample was not a typical relaxor ferroelectric. A polymorphic phase transition between rhombohedral and tetragonal phase was noticed near room temperature followed by a tetragonal to cubic transition with 97 degrees C as the temperature of maximum permittivity. The macroscopic values of d(33) and d(31) were similar to 350 pC/N and -141 pm/V, whereas the electromechanical coupling factors k(p) and k(t) were 44.5% and 41.6%, respectively. Bulk P-E hysteresis loop was obtained with saturation polarization 11 mu C/cm(2) and coercive field similar to 4 kV/cm. Distinct polarization contrast with a complex mosaic-like domain structure was observed in the out-of-plane mode of piezoresponse force microscopy. The domain width and the correlation length were estimated to be nearly 2 mu m and 827 nm, respectively. Local hysteresis loop with apparent coercive voltage, V-c = 15.8 V, was observed. (C) 2013 AIP Publishing LLC

A comparative study of structural and electrical properties in lead-free BCZT ceramics: Influence of the synthesis method

In the present work, various grain size phenomena were studied in promising lead-free piezoelectric ceramics (Ba0.85Ca0.15) (Zr0.10Ti0.90)O3 fabricated via chemical and conventional oxide methods. Phase composition was ascertained by the Rietveld refinement. Average grain size estimated from the microstructure was ∼1.5 μm in the sol-gel derived ceramic (SG-BCZT) which was much smaller than that obtained in coarse grained (∼27 μm) sample prepared by solid state method (SS-BCZT). Systematic investigation of various functional properties viz. dielectric, ferroelectric, piezoelectric and impedance emphasized the profound influence of grain size effects. The increase in grain boundary volume fraction enhanced diffuseness while lowered the dielectric peak in SG-BCZT. Similarly, increase in elastic stiffness and progressive hindrance to domain wall movements, resulted in a decrease of the remnant polarization and the associated piezoelectric charge coefficient values in small-grained SG-BCZT sample. Accordingly, higher Young's modulus value of 158.3 GPa was observed in SG-BCZT as compared to 117.9 GPa in SS-BCZT. Local-area piezoresponse force microscopy (PFM) images revealed lamellar domains with periodicity 250 ± 90 nm in SS-BCZT while small sized fractal-like irregular domains with an estimated domain width of 150 ± 60 nm were registered in SG-BCZT. Complex impedance spectroscopy results along with grain boundary conductivity were also guided by grain size effect. The mechanisms of grain size driven effects and their impact on the functional properties were discussed.publishe

Memory effect near transition temperature in Sm C* phase in nonsurface stabilized ferroelectric liquid crystals

Memory behavior in the ferroelectric liquid crystal � FLC � material, Felix 17/100, has been investigated by electro-optical, dielectric, and hysteresis methods at different temperatures ranging from room temperature to near ferro-paraelectric phase transition. Memory effect has been observed in the studied material near the transition temperature in Sm C � phase in the cells having thickness greater than the pitch value of the material. This is in contrast to the memory effect observed in conventional FLCs where thickness of the cell has to be less than the pitch value of the material. Electrical conductivity measurements elucidate that the steep increase in the conductivity near the transition temperature in Sm C* phase enhances the motion of free ions and probably weakens the depolarization field in the material, thereby showing memory effect

Low field magnetoresistance, temperature coefficient of resistance and magnetocaloric effect in Pr2/3Ba1/3MnO3:PdO composites

Electrical resistivity, magnetoresistance (MR), temperature coefficient of resistance (TCR) and magnetocaloric effect of (1 − x) Pr2/3Ba1/3MnO3:x PdO (x = 0–30 mol% PdO) composite manganites are reported here. Pristine sample Pr2/3Ba1/3MnO3 (PBMO) shows two insulator–metal like transitions (TP1 ~ 194 K and TP2 ~ 160 K) in the electrical resistivity behavior. With PdO, TP1 becomes sharper whereas TP2 disappears beyond 10 mol% PdO addition. The intrinsic MR gets enhanced from 22% for the pristine sample to ~ 42% for 27% PdO sample. However, the extrinsic MR is found to decrease in the composites. The TCR also increases from a negligible value for PBMO to 8% for 25 mol% PdO sample. These features have been explained on the basis of opening of new conducting channels and decrease in spin dependent scattering and the overall decrease in electrical resistivity. The magnetic entropy change and relative cooling power (RCP) for the PBMO sample are 5.3418 J.Kg-K and 304.5428 J/Kg respectively. However, these values decrease in the composites