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Title: Effect of bond fluctuations on the transport properties of manganites and nickelates

Abstract

For the manganites RMnO{sub 3} (R = La, Pr, Nd), a mechanism is proposed to explain the anomalous temperature dependences of the kinetic coefficients, resistivity, and thermoelectric power during the transition from the pseudocubic O to the orthorhombic O' crystal structure. The contributions of the bending and stretching modes of the octahedron to the formation of thermal-conductivity maxima and to the deviation from the linear dependence of ln({rho}/T) on 1/T at low temperatures have been estimated. In nickelates, the metal-insulator transition is caused by lattice-polaron pinning by the stretching mode of the octahedron, and the low-temperature anomaly of the thermal conductivity is related to electron scattering by the bending mode of the octahedron.

Authors:
 [1]
  1. Russian Academy of Sciences, Kirensky Institute of Physics, Siberian Division (Russian Federation), E-mail: apl@iph.krasn.ru
Publication Date:
OSTI Identifier:
21072476
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 104; Journal Issue: 5; Other Information: DOI: 10.1134/S1063776107050111; Copyright (c) 2007 Nauka/Interperiodica; Article Copyright (c) 2007 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ELECTRON DIFFRACTION; LANTHANUM COMPOUNDS; MANGANATES; NEODYMIUM COMPOUNDS; NICKELATES; ORTHORHOMBIC LATTICES; PRASEODYMIUM COMPOUNDS; TEMPERATURE DEPENDENCE; THERMAL CONDUCTIVITY

Citation Formats

Aplesnin, S. S. Effect of bond fluctuations on the transport properties of manganites and nickelates. United States: N. p., 2007. Web. doi:10.1134/S1063776107050111.
Aplesnin, S. S. Effect of bond fluctuations on the transport properties of manganites and nickelates. United States. doi:10.1134/S1063776107050111.
Aplesnin, S. S. Tue . "Effect of bond fluctuations on the transport properties of manganites and nickelates". United States. doi:10.1134/S1063776107050111.
@article{osti_21072476,
title = {Effect of bond fluctuations on the transport properties of manganites and nickelates},
author = {Aplesnin, S. S.},
abstractNote = {For the manganites RMnO{sub 3} (R = La, Pr, Nd), a mechanism is proposed to explain the anomalous temperature dependences of the kinetic coefficients, resistivity, and thermoelectric power during the transition from the pseudocubic O to the orthorhombic O' crystal structure. The contributions of the bending and stretching modes of the octahedron to the formation of thermal-conductivity maxima and to the deviation from the linear dependence of ln({rho}/T) on 1/T at low temperatures have been estimated. In nickelates, the metal-insulator transition is caused by lattice-polaron pinning by the stretching mode of the octahedron, and the low-temperature anomaly of the thermal conductivity is related to electron scattering by the bending mode of the octahedron.},
doi = {10.1134/S1063776107050111},
journal = {Journal of Experimental and Theoretical Physics},
number = 5,
volume = 104,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Five members of Ln{sub 5/8}M{sub 3/8}MnO{sub 3} series with A-cation size variance ({sigma}{sup 2}) ranging between 3x10{sup -4} and 71x10{sup -4}A{sup 2}, and the same A-cation size <r{sub A}>=1.2025A, have been synthesized by the ceramic method. The five manganites are single phase and they crystallize in the Pnma perovskite superstructure. The five compositions display ferromagnetic-paramagnetic transitions at temperatures ranging between 130 and 270K, for the highest and lowest variance sample, respectively. The samples with smaller variances show sharp magnetization transitions and the samples with the larger variances display broad transitions. These transitions have also been studied by differential scanning calorimetry,more » DSC, and some enthalpy changes are reported. The resistivity study indicates that all samples display the expected metal-to-insulator transitions at temperatures ranging between 140 and 270K. The samples have been analysed at room temperature by ultra-high-resolution synchrotron powder diffraction and the structural and microstructural features are reported. Furthermore, Nd{sub 5/8}Sr{sub 0.255}Ca{sub 0.12}MnO{sub 3} ({sigma}{sup 2}=40x10{sup -4}A{sup 2}) and Sm{sub 0.225}Nd{sub 0.4}Sr{sub 0.308}Ca{sub 0.067}MnO{sub 3} ({sigma}{sup 2}=53x10{sup -4}A{sup 2}) samples have also been studied by synchrotron powder diffraction at 140K, below the transition temperatures. Both samples are found to be single phase above and below the transition by ultra-high-resolution synchrotron powder diffraction. The microstructure of the samples has been investigated through Williamson-Hall plots. Sample broadenings are markedly anisotropic and strongly dominated by microstrains with average values of the {delta}d/d term close to 14x10{sup -4}. A direct correlation is found between the microstrain values and the widths of the magnetization transitions.« less
  • Using synchrotron x-ray scattering on single crystals of Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3} and La{sub 5/3}Sr{sub 1/3}NiO{sub 4}, we have demonstrated the existence of charge stripe structures in both compounds. In Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3} charge ordered satellite reflections were located at positions (h/20l), h=odd and l=even. In addition we have also observed some weak reflections at other positions (h/2kl/2) and (h/20l/2), h and l=odd and k=1. The result is in accord with the CE-type antiferromagnetic structure as reported by neutron powder diffraction. The transition was observed to be at a transition temperature T{sub CO}{approx_equal}159 K and to be strongly firstmore » order in nature. By contrast, studies of La{sub 5/3}Sr{sub 1/3}NiO{sub 4} showed a second order transition at T{sub CO}{approx_equal}240 K. This produced charge stripe satellites with a wavevector q=(h{+-}2{epsilon}0l), h=even and l=odd. Critical exponents of the transition were obtained and show that the system is in the 2D universality class. The two dimensional nature of the charge stripes is clearly shown in their markedly different correlation lengths at low temperatures e.g., {xi}{sub a}{approx_equal}110 A, {xi}{sub b}{approx_equal}130 A, whist {xi}{sub c} is only about 17 A. These results demonstrate clearly that the charge stripes are themselves two dimensional in character.« less
  • No abstract prepared.
  • The time-dependent Ginzburg-Landau theory is used to study both transverse and longitudinal transport properties of a layered superconductor in a magnetic field near the mean-field transition temperature {ital T}{sub {ital c}2}({ital H}). We evaluate the transport coefficients in the self-consistent Hartree approximation which interpolates smoothly between the high-temperature regime, dominated by Gaussian fluctuations, and the low-temperature flux-flow regime, with no intervening divergence. This behavior is in agreement with the experimental results for the Ettingshausen coefficient, Nernst coefficient, longitudinal conductivity, and Hall conductivity in high-temperature superconductors.
  • In Ce-doped RMnO{sub 3} the rare earth (R) is partially replaced with cerium ions instead of divalent alkaline-earth metals. These compounds are very sensitive to annealing. The resistivity and thermoelectric power (TEP, S) of R{sub 0.7}Ce{sub 0.3}MnO{sub 3} (R=La, Pr, and Nd) have been studied as a function of annealing conditions. They show a ferromagnetic to paramagnetic transition, and a resistive peak near T{sub c}, marking a metal-insulator (MI) transition. A pronounced giant magnetoresistance effect is also observed in these compounds, and T{sub c} can be changed by annealing in various atmospheres. The {rho}(T) curve of oxygen overdoped samples showsmore » double peaks along with a hysteresis loop (in the heating and cooling cycles), which bears the signature of the first-order nature of the transition. The thermopower of as-prepared samples show a peak near the MI transition, and changes sign from positive to negative at temperatures below the ferromagnetic transition. The magnitude of S at low temperatures is enhanced to an abnormally large value. With increasing of oxygen content, several characteristic features develop in the temperature dependence of the thermopower which is consistent with the resistive behavior. At high temperatures, the resistivity and thermopower follow the predictions of the Emin-Holstein theory of adiabatic polaron hopping. {copyright} {ital 1997} {ital The American Physical Society}« less