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B4C in ex-situ spark plasma sintered MgB2
M. Burdusel,G. Aldica,S. Popa,M. Enculescu,V. Mihalache,A. Kuncser,I. Pasuk,P. Badica 한국물리학회 2015 Current Applied Physics Vol.15 No.10
Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C)x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 ℃ for 3 min. The average particle size of B4C raw powder was relatively high of 4 mm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density Jc at high magnetic fields and of the irreversibility field Hirr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a Jc of 100 A/cm2 is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions.
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Sub-lattice polarization states in anti-ferroelectrics and their relaxation process
M.M. Vopson,X. Tan,E. Namvar,M. Belusky,S.P. Thompson,V. Kuncser,F. Plazaola,I. Unzueta,C.C. Tang 한국물리학회 2019 Current Applied Physics Vol.19 No.4
We report studies of quasi-remanent polarization states in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 (PNZST) anti-ferroelectric ceramics and investigation of their relaxation effects using unique in-situ electrically activated time-resolved Synchrotron X-ray powder diffraction (SXPD) and 119Sn Mössbauer Spectroscopy (MS). The SXPD patterns are consistent with a phase transition from quasi-tetragonal perovskite in 0 V relaxed anti-ferroelectric state to rhombohedral distortion in ferroelectric state under saturating applied voltages of±2 kV. The observed quasi-remanent polarization relaxation processes are due to the fact that tetragonal to rhombohedral distortion does not occur at the applied voltage required to access the quasi-remanent polarization states, and the tetragonal symmetry restored after the removal of the applied electric field is preserved. Since these quasi-remanent polarization states were seen as possibly suitable for memory applications, the implications of this study are that anti-ferroelectrics are more feasible for multi-state dynamic random access memories (DRAM), while their application to non-volatile memories requires development of more sophisticated “read-out” protocols, possibly involving dc electrical biasing.
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