Magnetic, electrical, and thermal characterization of La0.9Te0.1Mn1−xCoxO3 (0 ≤ x ≤ 1)

2007 ◽  
Vol 22 (10) ◽  
pp. 2943-2952
Author(s):  
R. Ang ◽  
Y.P. Sun ◽  
G.H. Zheng ◽  
W.H. Song
Keyword(s):  
Temperature Dependence ◽  
Temperature Region ◽  
Configurational Entropy ◽  
Thermal Characterization ◽  
Measured Temperature ◽  
Magnetic Exchange ◽  
Space Group ◽  
Co Doping ◽  
Jahn Teller ◽  
Anomalous Peak

The structure, magnetization M, resistivity ρ, thermoelectric power S, and thermal conductivity κ in La0.9Te0.1Mn1−xCoxO3 (0 ≤ x ≤ 1) have been investigated systematically. The samples with x = 0 and x = 1 have a rhombohedral lattice with space group R¯3C, while the samples with x = 0.25, 0.50, and 0.75 have an orthorhombic lattice with space group Pbnm. The samples of 0 ≤ x ≤ 0.75 undergo the paramagnetic–ferromagnetic (PM–FM) phase transition. Based on the temperature dependence of susceptibility, a combination of the high-spin (HS) state for Co2+ and the low-spin (LS) state for Co3+ can be determined. The metal–insulator transitions (MIT) observed for x = 0 sample are completely suppressed with Co-doping, and ρ(T) displays semiconducting behavior within the measured temperature region for x > 0 samples. As x ⩾ 0.25, the huge magnitude of Seebeck coefficient at low temperatures is observed, which is suggested to originate from the spin-state transition of Co3+ ions from intermediate-spin (IS) state or (HS) state to (LS) state and the configurational entropy of charge carriers enhanced by their spin and orbital degeneracy between Co2+ and Co3+ sites. Particularly, S(T) of x = 0.50 and 0.75 samples appears an anomalous peak, which is suggested to be related to the contribution of phonon drag. Similar to M(T) and ρ(T), all results of S(T) are discussed according to the variations of the structure parameters and magnetic exchange interaction caused by Co-doping. In addition, based on the analysis of the temperature dependence of S(T) and ρ(T), the transport mechanism can be determined in the different temperature region. As to thermal conduction κ(T), the changes of κ with Co-doping is suggested to come from the combined effect due to the suppression of local Mn3+O6 Jahn–Teller (JT) lattice distortion because of the substitution of non JT Co3+ ions with LS and HS states for JT Mn3+ ions, which results in the increase of κ, and the introduction of the disorder due to Co-doping, which contributes to the decrease of κ.

Phononenassistierte Auger-Prozesse in III–V-Verbindungen / Phononassisted Auger Processes in III–V-Compounds

1973 ◽  
Vol 28 (8) ◽  
pp. 1233-1246 ◽  
Author(s):  
Wolfgang Rosenthal
Keyword(s):  
Temperature Dependence ◽  
Temperature Region

Phononassisted Augerprocesses are investigated as a mechanism of band-to-band-transitions in III-V-Compounds. It is found that they can explain the temperature dependence in a temperature region, where the normal Auger processes are ineffective.

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

Structures and Phase Transitions of the A 7PSe6 (A = Ag, Cu) Argyrodite-Type Ionic Conductors. I. Ag7PSe6

1998 ◽  
Vol 54 (4) ◽  
pp. 376-383 ◽  
Author(s):  
M. Evain ◽  
E. Gaudin ◽  
F. Boucher ◽  
V. Petricek ◽  
F. Taulelle
Keyword(s):  
Phase Transition ◽  
Atomic Displacement ◽  
Ionic Conductors ◽  
Reliability Factor ◽  
Conducting Phase ◽  
Cubic Symmetry ◽  
Space Group ◽  
Ionic Conducting ◽  
Jahn Teller ◽  
Diffusion Paths

The crystal structures of the two polymorphic forms of the argyrodite Ag7PSe6 compound are analysed by means of single-crystal X-ray diffraction. Above the phase transition at 453 K leading to the ionic conducting phase, γ-Ag7PSe6 crystallizes in cubic symmetry, space group F4¯3m, with a = 10.838 (3) Å, V = 1273.1 (12) Å3 and Z = 4 at 473 K. The refinement of the 473 K structure leads to a reliability factor of R = 0.0326 for 192 independent reflections and 33 variables. Diffusion paths for silver d 10 ions are evidenced by means of a combination of a Gram–Charlier development of the atomic displacement factors and a split model. Below the phase transition β-Ag7PSe6 crystallizes again in cubic symmetry, but with the space group P213 and a = 10.772 (2) Å, V = 1250.1 (6) Å3 and Z = 4 at room temperature. The refinement of the 293 K structure leads to a reliability factor of R = 0.0267 for 1125 independent reflections and 68 variables. In the β-Ag7PSe6 ordered phase the silver cations are found in various sites corresponding to the most pronounced probability density locations of the high-temperature diffusion paths. Those positions correspond to low coordination (2, 3 and 4) sites, in agreement with the silver preference for such environments. In addition, the Ag atoms are found slightly displaced from the true linear, triangular or tetrahedral coordination, as expected from second-order Jahn–Teller effects.

Silver Self-Diffusion in Al2O3/QE22 Magnesium Alloy Matrix Composite

2009 ◽  
Vol 283-286 ◽  
pp. 155-160
Author(s):  
Ivo Stloukal ◽  
Jiří Čermák
Keyword(s):  
Magnesium Alloy ◽  
Temperature Dependence ◽  
Temperature Interval ◽  
Matrix Composite ◽  
Diffusion Coefficients ◽  
Volume Diffusion ◽  
Effective Diffusion ◽  
Measured Temperature ◽  
Alloy Matrix ◽  
Self Diffusion

Self-diffusion of 110mAg has been investigated in fiber reinforced QE22 magnesium alloy matrix composite. Short Saffil fibers (97% -Al2O3 + 3% SiO2) were used as reinforcement. The diffusion measurements were carried out in the temperature interval 648 – 728 K by serial sectioning method. The volume diffusion coefficients Dv (alloy without reinforcement) and the effective diffusion coefficients Deff (alloy with reinforcement) were obtained by analysis of the penetration curves. The silver diffusion coefficient in the interface boundary matrix/Saffil Di was also estimated. The temperature dependence of volume diffusion coefficients Dv was compared with previous data measured using 65Zn in the same alloy and with literature data for Zn impurity diffusion in Mg single crystal. It was observed, that the temperature dependence of both Deff and Di was significantly non-linear in the measured temperature interval. This behavior supports previous observations with zinc diffusion in the same alloy.

Optical Spectroscopy of Mixed Metamagnetic FexCo1-xCl2 Crystals

1980 ◽  
Vol 35 (10) ◽  
pp. 1013-1019 ◽  
Author(s):  
Friedrich Seitz ◽  
Terence E. Wood ◽  
Peter Day
Keyword(s):  
Charge Transfer ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Absorption Spectra ◽  
Optical Spectroscopy ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Broad Band ◽  
Mixed Crystals ◽  
Magnetic Exchange

Abstract Electronic absorption spectra are reported for single crystals of composition FexCo1-xCl2 as a function of temperature from 300 K to 4 K. A broad band at 436 nm is assigned to Fe (II) → Co (II) charge transfer and the temperature dependence of its intensity is related to the magnetic exchange between the ions. The 2T1g(2H) excitation of Co (II) in the mixed crystals has an unusual temperature dependence which correlates with the Néel temperature.

High Pressure Reactions in the Systems Zn3As2—As and Cd3As2—As

1975 ◽  
Vol 30 (9-10) ◽  
pp. 688-695 ◽  
Author(s):  
J. B. Clark ◽  
Klaus-Jürgen Range
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Temperature Region ◽  
High Temperature Region ◽  
Orthorhombic Space Group ◽  
Decomposition Products ◽  
High Pressure And Temperature ◽  
Space Group ◽  
Group D

ZnAs2 and CdAs2 decompose at high pressure and temperature. The determined decomposition boundaries are presented. From synthesis experiments in the systems Cd3As2—As and Zn3As2—As, the decomposition products were found to be mixtures of CdAs + As and ZnAs + As. The high pressure phases CdAs and ZnAs are orthorhombic, space group D152h — Pbca, with αo = 5.993 A, bo = 7.819 A, co = 8.010 Å and αo = 5.679 A, bo = 7.277 A, co = 7.559 Å, respectively. Further phases are recovered from the high temperature region at high pressure.

scholarly journals Über die Strukturen der CuZrF6-Modifikationen - Neutronenbeugungsuntersuchungen an den Kristallpulvern / A Neutron Diffraction Study on the Modifications of CuZrF6

1978 ◽  
Vol 33 (3) ◽  
pp. 268-274 ◽  
Author(s):  
V. Propach ◽  
F. Steffens
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Experimental Evidence ◽  
Neutron Diffraction Study ◽  
Three Dimensions ◽  
Space Group ◽  
Powder Samples ◽  
Jahn Teller ◽  
Jahn Teller Effect

Abstract The structures of two modifications of CuZrF6 by means of neutron diffraction on powder samples in the temperature range from 298-560 K are reported. All modifications consist of octahedra, which share corners in three dimensions and which are centered alternately by Cu2+ or Zr4+. The high temperature α-modification crystallizes in space group Fm3 (No. 202) with α = 7.939 Å. There is experimental evidence, that the CuFe-octahedra are distorted by a static Jahn-Teller-effect. The space group P1̄ (No. 2) with Z = 2 is proposed for the low-temperature γ-modification.

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