1,457 research outputs found
A Detailed XRD and FTIR Analysis of Bi2O3 Doped ZnO-SnO2 Ceramics
Poster presented at the 2nd International Congress on Ceramics, Verona, Italy, June 29 - July 4, 200
Evidences for Tsallis non-extensivity on CMR manganites
We found, from the analysis of vs. curves of some manganese oxides
(manganites), that these systems do not follow the traditional
Maxwell-Boltzmann statistics, but the Tsallis statistics, within the
\QTR{em}{normalized} formalism. Curves were calculated within the mean field
approximation, for various ferromagnetic samples and the results were compared
to measurements of our own and to various other authors published data, chosen
at random from the literature. The agreement between the experimental data and
calculated vs. curve, where is an effective
temperature, is excellent for all the compounds. The entropic parameter, ,
correlates in a simple way with the experimental value of , irrespect
the chemical composition of the compounds, heat treatment or other details on
sample preparation. Examples include (superextensivity),
(extensivity) and (subextensivity) cases.Comment: 12 pages, 3 figure
Structure inhomogeneities, shallow defects, and charge transport in the series of thermoelectric materials K2Bi8āxSbxSe13
The charge transport properties of the low-dimensional thermoelectric materials K2Bi8-xSbxSe13 (02Bi8-xSbxSe13 was analyzed on the basis of the classical semiconductor theory and discussed in the context of recent band calculations. The results suggest that the K2Bi8-xSbxSe13 materials possess coexisting domains with semimetallic and semiconducting characters whose ratio is influenced by the value of x and by local defects. The extent and relative distribution of these domains control the charge transport properties. Electron diffraction experiments performed on samples of K2Bi8-xSbxSe13 with x=1.6 show evidence for such domains by indicating regions with long range ordering of K+/Bi3+ atoms and regions with increased disorder. The semiconducting behavior is enhanced with increasing x (i.e., Sb/Bi ratio) in the composition through a decrease of the semimetallic fraction
Changes of Structural, Optical and Electrical Properties of Nickel-Manganite Ceramics Induced by Additional Mechanical Activation
Poster presented at the 10th International Conference and Exhibition of the European Ceramic Society, Berlin, June 17-21, 200
Crystal Field and Dzyaloshinsky-Moriya Interaction in orbitally ordered La_{0.95}Sr_{0.05}MnO_3: An ESR Study
We present a comprehensive analysis of Dzyaloshinsky-Moriya interaction and
crystal-field parameters using the angular dependence of the paramagnetic
resonance shift and linewidth in single crystals of La_{0.95}Sr_{0.05}MnO_3
within the orthorhombic Jahn-Teller distorted phase. The Dzyaloshinsky-Moriya
interaction (~ 1K) results from the tilting of the MnO_6 octahedra against each
other. The crystal-field parameters D and E are found to be of comparable
magnitude (~ 1K) with D ~= -E. This indicates a strong mixing of the |3z^2-r^2>
and |x^2-y^2> states for the real orbital configuration.Comment: 12 pages, 6 figure
Interplay of superexchange and orbital degeneracy in Cr-doped LaMnO3
We report on structural, magnetic and Electron Spin Resonance (ESR)
investigations in the manganite system LaMn_{1-x}Cr_{x}O_{3} (x<=0.5). Upon
Cr-doping we observe a reduction of the Jahn-Teller distortion yielding less
distorted orthorhombic structures. A transition from the Jahn-Teller distorted
O' to the pseudocubic O phase occurs between 0.3<x<0.4. A clear connection
between this transition and the doping dependence of the magnetic and ESR
properties has been observed. The effective moments determined by ESR seem
reduced with respect to the spin-only value of both Mn^{3+} and Cr^{3+} ions
Structural, magnetic and electrical properties of single crystalline La_(1-x)Sr_xMnO_3 for 0.4 < x < 0.85
We report on structural, magnetic and electrical properties of Sr-doped
LaMnO_3 single crystals for doping levels 0.4 < x < 0.85. The complex
structural and magnetic phase diagram can only be explained assuming
significant contributions from the orbital degrees of freedom. Close to x = 0.6
a ferromagnetic metal is followed by an antiferromagnetic metallic phase below
200 K. This antiferromagnetic metallic phase exists in a monoclinic
crystallographic structure. Following theoretical predictions this metallic
antiferromagnet is expected to reveal an (x^2-y^2)-type orbital order. For
higher Sr concentrations an antiferromagnetic insulator is established below
room temperature.Comment: 8 pages, 7 figure
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