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High Curie Temperature (high + curie_temperature)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Physical and Electrical Properties of Nanosized Mn- and Cr-Doped Strontium Y-Type Hexagonal Ferrites

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010
Muhammad Javed Iqbal
Nanometer-sized crystallites of Y-type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn- and Cr-doped derivatives have been synthesized by the sol,gel method. Y-type phase formation was achieved at a considerably lower temperature of 950°C than is required in the traditional solid-state method (1200°C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2,xMnx Fe12O22 (x=0.0,2.0), and chromium at octahedral site, Sr2Ni2 Fe12,yCryO22 (y=0.0,1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13,45 nm is calculated from the X-ray diffraction data. The energy-dispersive X-ray fluorescence analysis shows that Y-type hexaferrites can be prepared with a base of strontium. The extent of doped Cr+3 ions at the octahedral site has been increased from the reported maximum value of y=1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr-doped samples have comparatively higher resistivity than Mn-doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 × 109,-cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples. [source]

Addition of a Sr, K, Nb (SKN) Combination to PZT(53/47) for High Strain Applications

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007
Niall J. Donnelly
A lead zirconate titanate composition incorporating the dopants Sr, K, and Nb (SKN) in the specific ratio 4:1:3 has been studied. In principle, the SKN should act as a donor dopant but since its addition reduced the grain size from 11.4 ,m (for 1% SKN) to 1.5 ,m (for 5% SKN), the overall effect was found to be more complicated. It was observed that the addition of SKN reduced the Curie temperature, by 16°C/mol (%) and broadened the dielectric peak. X-ray measurements further suggested that the ceramic was a mixture of rhombohedral and tetragonal phases and that the room temperature c/a ratio of the tetragonal phase decreased with SKN addition. The piezoelectric coefficient d33, determined from high field unipolar drives, gave an optimum value of 779 pm/V for the 0.02 SKN compositions, which also exhibited a relatively high Curie temperature of 356°C. Competing effects of enhanced domain wall mobility from donor doping and reduced mobility due to smaller grain size may explain the observed compositional variation in the measured material properties. Materials based on this composition are attractive for high performance piezoelectric actuator applications such as fuel injection. [source]

Microstructure and electrical properties of (1,x)(K0.5Na0.5)NbO3,x BiFeO3 piezoelectric ceramics

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008
Xiang Li
Abstract Lead,free ceramics (1,x)(K0.5Na0.5)NbO3,x BiFeO3 doped with 1 mol% Fe2O3 (KNNBF/x) have been synthesized by pressureless sintering. With the Fe2O3 doping, the KNNBF/x ceramics can be well sintered at 1085,1100 °C and exhibit a pure perovskite structure with x < 0.013. It was found that the crystal structure of the KNNBF/x ceramics changed from orthorhombic to tetragonal and then to pseudocubic phase with the increase of BiFeO3 content. The composition KNNBF/0.013 near the tetragonal symmetry that separates the orthorhombic and pseudocubic phases exhibits improved electrical properties: d33 = 173 pC/N, kp = 0.40, ,r = 905, tan , = 4%, Pr = 26 ,C/cm2, and Ec = 11.2 kV/cm, with a high Curie temperature (TC) of about 388 °C. Our results suggest that KNNBF/x are promising lead-free high temperature piezoelectric ceramics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electronic structure and magnetic properties of Cu-doped SnO2 from first-principles study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2009
Chang-wen Zhang
Abstract We have studied the electronic structure of Cu-doped SnO2, with different possible geometrical sites for the Cu dopant, to determine the most favored magnetic properties. Our study shows that each Cu has spin-polarized states in the band gap generating a magnetic moment 2.0,B. We also find Cu impurities tend to form clusters which induces strong ferromagnetism with high Curie temperature, through the same p,d hopping interactions as found in Sr2FeMoO6 [Phys. Rev. Lett. 85, 2549 (2000)]. Doped p-type carriers enhanced the ferromagnetism, while n-type carriers are detrimental to ferromagnetism due to charge compensating effects, indicating that the strong ferromagnetism in Cu-doped SnO2 would be achieved by hole doping. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]