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73 results on '"Kopnin, E.M."'

39. Influence of humidity and thermal decomposition on the protonic conductivity of single and polycrystalline CsH2PO4

Author

Baranov, A.I., Kopnin, E.M., Grebenev, V.V., Sin, A., Zaopo, A., Dubitsky, Yu., and Caracino, P.

Subjects
*HYGROMETRY, *HUMIDITY, *PROTONS, *ELECTRIC conductivity
Abstract

Abstract: The influence of the preparation conditions and metaphosphate secondary phase on the proton conduction and chemical stability of the single and polycrystalline CsH2PO4 samples was studied by the ac admittance technique. The relation between frequency dependences of the admittance plots and adsorbed water as well as a content of the metaphosphate phase was determined. It was shown that in ambient conditions the thermal decomposition reactions start on the sample''s surface at temperatures above specific point, T 1 =425 K, and the rate of the decomposition reactions on the interfaces is strongly influenced by the sample''s quality. It is suggested that this reaction is initiated by the melting of the thin layer of CsH5(PO4)2 on the surface of CsH2PO4. The variation of the contributions of the intergrain and electrode–proton conductor boundaries to the total admittance with the temperature was studied for polycrystalline CDP samples and obtained data were compared with those for nominally pure CDP single crystal samples. [Copyright &y& Elsevier]

Published
2007
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40. Synthesis, crystal structure, and magnetic properties of new layered hexagonal perovskite Ba8Ta4Ru8/3Co2/3O24

Author

Kopnin, E.M., Belik, A.A., Shpanchenko, R.V., Antipov, E.V., Izumi, F., Takayama-Muromachi, E., and Hadermann, J.

Subjects
*PARTICLES (Nuclear physics), *PEROVSKITE, *ELECTRON diffraction, *NEUTRON diffraction
Abstract

A new hexagonal perovskite-type oxide Ba8Ta4Ru8/3Co2/3O24 was synthesized by the solid-state method at 1573 K and characterized by electron diffraction (ED), time-of-flight (TOF) neutron powder diffraction, and magnetic susceptibility. Structure parameters of Ba8Ta4Ru8/3Co2/3O24 were refined by the Rietveld method from the TOF neutron powder diffraction data on the basis of space group P63/mcm and lattice parameters a=10.0075(1) Å and c=18.9248(2) Å as obtained from the ED data (Z=3). The crystal structure of Ba8Ta4Ru8/3Co2/3O24 consists of 8-layered (cchc)2 close-packed stacking of BaO3 layers along the c-axis. Corner-shared octahedra are filled by Ta only and face-shared octahedra are statistically occupied by Ru, Co, and vacancies. Similar compounds Ba8Ta4Ru8/3M2/3O24 with M=Ni and Zn were also prepared. Magnetic susceptibility measurements showed no magnetic ordering down to 5 K. [Copyright &y& Elsevier]

Published
2004
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41. High-pressure synthesis and crystal structures of B2Sr3(Y,Sr)2Cu3O12 and B2Sr3(Ho,Sr)2Cu3O12

Author

Kopnin, E.M., Akiyoshi, M., Sato, A., Matsui, Y., and Takayama-Muromachi, E.

Subjects
*BORATES, *CRYSTALS, *ELECTRON scattering
Abstract

Two new layered oxyborates B2Sr3.2Y1.8Cu3O12 and B2Sr3.11Ho1.89Cu3O12 have been synthesized at 6 GPa using a belt-type apparatus. These compounds could be described as intergrowth between B-1201 and B-1212 phases. The crystal structure of B2Sr3.11Ho1.89Cu3O12 has been determined using single crystal X-ray data. It was refined to R1(I>2σ(I))=0.0456, wR2(all data)=0.1044 with F2 data. B2Sr3.2Y1.8Cu3O12 and B2Sr3.11Ho1.89Cu3O12 crystallize in the space group P4/mmm (no. 123), Z=1 with a=3.852(1) A˚, c=17.770(6) A˚ and a=3.8516(4) A˚, c=17.764(2) A˚, respectively. A weak superstructure with as=a√2, bs=b√2, cs=c was deduced from an electron diffraction pattern for B2Sr3.11Ho1.89Cu3O12 probably due to local ordering of the triangular BO3 groups although such ordering was not revealed from single crystal X-ray data. [Copyright &y& Elsevier]

Published
2003
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42. Critical current densities and irreversibility fields of high-<f>Tc</f> superconductors AuBa2Can−1CunO2n+3 <f>(n=3,4)</f> prepared under high pressure

Author

Yu, S., Kopnin, E.M., and Takayama-Muromachi, E.

Subjects
*CRITICAL currents, *SUPERCONDUCTORS, *HIGH pressure chemistry, *HYSTERESIS, *ELECTRONIC structure
Abstract

Critical current densities (Jc) and irreversibility fields (Birr) of high-Tc superconductors AuBa2Can−1CunO2n+3 [Au-12(n−1)n, n=3,4] prepared under high pressure were determined from the hysteresis in DC magnetization loop. Both the Jc and Birr values of the Au-1234 phase were larger than those of Hg- and Bi-based cupurate superconductors, but smaller than those of the Y-123 superconductor. This result suggests that the electronic structure of Au-1234 is less anisotropic compared with the Hg- and Bi-phases. The Au-1223 phase showed very small Jc values corresponding to its small superconducting volume fraction. [Copyright &y& Elsevier]

Published
2003
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43. Structure analysis of Au-containing cuprate of Au<f>1+x</f>Ba2Ca2Cu<f>3−x</f>O9 (Au-1223)

Author

Kopnin, E.M., Sato, A., Asaka, T., Matsui, Y., and Takayama-Muromachi, E.

Subjects
*CRYSTALS, *COPPER compounds, *SUPERCONDUCTIVITY
Abstract

Single crystals of Au1+xBa2Ca2Cu3−xO9 (Au-1223) were grown at 6 GPa and 1325 °C. This phase is the third member of the Au-containing cuprate family of AuBa2Can−1CunO2n+3 and shows a weak signal of superconductivity. The crystal structure was refined to R1 (I>2σ(I))=0.0188 and wR2=0.0485 with F2 data. The Au-1223 phase crystallizes in the space group Pmmm (no. 47), a=3.8119(1) A˚, b=3.8556(1) A˚, c=15.4431(5) A˚, Z=1. Partial substitution of Au for Cu in the CuO2 planes was revealed. The Au incorporation to the conduction layers may be a reason for the suppression of superconductivity in Au-1223. [Copyright &y& Elsevier]

Published
2003
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44. Crystal structures of CCa2CuO5 and CSr1.9Ca1.1Cu2O7 refined from single crystal data

Author

Kopnin, E.M., Matveev, A.T., Salamakha, P.S., Sato, A., and Takayama-Muromachi, E.

Subjects
*CRYSTALS, *X-ray diffractometers, *SUPERCONDUCTIVITY
Abstract

Single crystals were grown for new layered oxycarbonates CCa2CuO5 and CSr1.9Ca1.1Cu2O7 at 6 GPa using a belt-type apparatus. Their crystal structures were determined using single crystal X-ray diffraction data with R1(wR2)=0.0294(0.0659) and 0.0199(0.0457) for CCa2CuO5 and CSr1.9Ca1.1Cu2O7, respectively. These phases crystallize in the space group P4/mmm (No. 123), Z=1 with a=3.8157(1) A˚, c=7.1426(3) A˚ for CCa2CuO5 and a=3.8753(1) A˚, c=10.6765(5) A˚ for CSr1.9Ca1.1Cu2O7. In contrast to CSr2CuO5, no ordering in the orientation of the triangular CO3 groups was revealed in CCa2CuO5 and CSr1.9Ca1.1Cu2O7. [Copyright &y& Elsevier]

Published
2003
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46. Synthesis and properties of NbM2RCu2O8and TaM2RCu2O8phases (MBA, Sr: RPr, Nd, Sm, Eu and Gd)

Author

Kopnin, E.M., Lobanov, M.V., Abakumov, A.M., Lubarskii, S.V., Lebedev, O.I., Antipov, E.V., and Capponi, J.J.

Abstract

NbM2RCu2O8and TaM2RCu2O8(MBa, Sr; RPr, Nd, Sm, Eu and Gd) phases were synthesized. Electron diffraction study of TaSr2EuCu2O8showed the presence of a weak superstructure (a= 82a07), like that found for a number of similar phases. Rietveld refinement of this structure based on X-ray powder diffraction data was carried out in the space groupP4/mmm(R1= 0.038, Rp= 0.037) since no superstructure reflections were observed. Various types of cation replacement were performed in order to increase the copper valence. Monophasic Nb(Ta)1, Ti,Sr2EuCu2O8samples were synthesized atP(O2) = 1 bar andT= 1050°C up tox= 0.1 (Nb) and 0.3 (Ta), but no superconductivity was detected down to 12 K. High pressure syntheses were carried out to obtain Nb(Ta)Sr2Eu1, Ca, Cu2O8phases, but they were found to have a narrow homogeneity range that provides no opportunity of inducing superconductivity in such a way.

Published
1996
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49. Ca1−xRxCuO2(R = Sr, La) single crystals with infinite-layer structure: high Ar gas pressure synthesis and properties.

Author

Kopnin, E.M., Schwer, H., Jun, J., Meijer, G.I., Molinski, R., Conder, K., and Karpinski, J.

Abstract

Single crystals CaCuO2, Ca1−xLaxCuO2and Sr0.53Ca0.47CuO2with inifinite-layer structure were synthesized using high Ar pressure. Magnetization measurements showed weak diamagnetism only in CaCuO2probably due to some A-deficient domains. A weak diamagnetic response was also revealed in a Sr0.53Ca0.47CuO2powder sample. However, superconductivity was not observed by resistivity measurements.

Published
1997
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