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Title: Temperature- and pressure-driven spin-state transitions in LaCoO{sub 3}

Abstract

Crystal structure, spin state, and semiconductor-metal transitions of LaCoO{sub 3} in the 10-905 K temperature range were studied by neutron diffraction at high pressures up to 4.5 GPa and x-ray diffraction and Raman spectroscopy at high pressures up to 17.5 GPa. The susceptibility and thermal-expansion anomalies in the studied pressure range can be described successfully by the thermal excitation of two orbitally nondegenerate magnetic states with different electronic configuration, intermediate spin (IS), and high spin (HS) from the low-spin (LS) nonmagnetic ground state. The pressure-induced compression of Co-O bonds leads to a substantial increase of LS-IS and LS-HS energy splittings E{sub 1} and E{sub 2} with d ln E{sub 1}/dP=0.37 and d ln E{sub 2}/dP=0.23 GPa{sup -1}. The onset of the semiconductor-metal (S-M) transition in LaCoO{sub 3} correlates with the vanishing of several Raman modes forbidden for rhombohedral R3c symmetry and originating from local distortions due to short-range e{sub g}-orbital order of IS Co{sup 3+} ions. The S-M transition temperature increases rapidly under pressure with dT{sub S-M}/dP{approx_equal}50 K/GPa.

Authors:
; ;  [1];  [2];  [3];  [4];  [5];  [6]
  1. Frank Laboratory of Neutron Physics, JINR, 141980 Dubna (Russian Federation)
  2. Institute of Physics, Cukrovarnicka 10, 162 53 Prague 6 (Czech Republic)
  3. Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D-95440 (Germany)
  4. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxon, OX11 0QX (United Kingdom)
  5. Physique des Milieux Condenses, Universite P and M Curie, B77, 4 Place Jussieu, 75252 Paris (France)
  6. Russian Research Center 'Kurchatov Institute', 123182 Moscow (Russian Federation)
Publication Date:
OSTI Identifier:
20976689
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevB.75.064422; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CALCIUM NITRIDES; COBALT IONS; ELECTRONIC STRUCTURE; EXCITATION; GROUND STATES; LANTHANUM COMPOUNDS; MAGNETIC SUSCEPTIBILITY; NEUTRON DIFFRACTION; PARAMAGNETISM; PRESSURE RANGE GIGA PA; PRESSURE RANGE MEGA PA 10-100; RAMAN SPECTRA; RAMAN SPECTROSCOPY; SEMICONDUCTOR MATERIALS; SPIN; THERMAL EXPANSION; TRANSITION ELEMENTS; TRANSITION TEMPERATURE; TRIGONAL LATTICES; X-RAY DIFFRACTION

Citation Formats

Kozlenko, D. P., Golosova, N. O., Savenko, B. N., Jirak, Z., Dubrovinsky, L. S., Tucker, M. G., Le Godec, Y., and Glazkov, V. P. Temperature- and pressure-driven spin-state transitions in LaCoO{sub 3}. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.064422.
Kozlenko, D. P., Golosova, N. O., Savenko, B. N., Jirak, Z., Dubrovinsky, L. S., Tucker, M. G., Le Godec, Y., & Glazkov, V. P. Temperature- and pressure-driven spin-state transitions in LaCoO{sub 3}. United States. doi:10.1103/PHYSREVB.75.064422.
Kozlenko, D. P., Golosova, N. O., Savenko, B. N., Jirak, Z., Dubrovinsky, L. S., Tucker, M. G., Le Godec, Y., and Glazkov, V. P. Thu . "Temperature- and pressure-driven spin-state transitions in LaCoO{sub 3}". United States. doi:10.1103/PHYSREVB.75.064422.
@article{osti_20976689,
title = {Temperature- and pressure-driven spin-state transitions in LaCoO{sub 3}},
author = {Kozlenko, D. P. and Golosova, N. O. and Savenko, B. N. and Jirak, Z. and Dubrovinsky, L. S. and Tucker, M. G. and Le Godec, Y. and Glazkov, V. P.},
abstractNote = {Crystal structure, spin state, and semiconductor-metal transitions of LaCoO{sub 3} in the 10-905 K temperature range were studied by neutron diffraction at high pressures up to 4.5 GPa and x-ray diffraction and Raman spectroscopy at high pressures up to 17.5 GPa. The susceptibility and thermal-expansion anomalies in the studied pressure range can be described successfully by the thermal excitation of two orbitally nondegenerate magnetic states with different electronic configuration, intermediate spin (IS), and high spin (HS) from the low-spin (LS) nonmagnetic ground state. The pressure-induced compression of Co-O bonds leads to a substantial increase of LS-IS and LS-HS energy splittings E{sub 1} and E{sub 2} with d ln E{sub 1}/dP=0.37 and d ln E{sub 2}/dP=0.23 GPa{sup -1}. The onset of the semiconductor-metal (S-M) transition in LaCoO{sub 3} correlates with the vanishing of several Raman modes forbidden for rhombohedral R3c symmetry and originating from local distortions due to short-range e{sub g}-orbital order of IS Co{sup 3+} ions. The S-M transition temperature increases rapidly under pressure with dT{sub S-M}/dP{approx_equal}50 K/GPa.},
doi = {10.1103/PHYSREVB.75.064422},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 6,
volume = 75,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • A uniaxial compression test of polycrystalline lanthanum cobaltite (LCO) was performed to investigate mechanical behavior of LCO in the temperature range of 83–553 K. Prepared by solid-state reaction, the electrical resistivity and the linear expansion coefficient of polycrystalline LCO, measured between 80 and 1273 K, exhibit distinct changes attributed to spin-state transitions of cobalt ions around 100–200 K and 400–600 K, but are relatively constant between 200 and 400 K. The stress-strain curve obtained under uniaxial compression shows strong nonlinearity due to ferroelastic domain switching process between 83 and 553 K. Initial Young's moduli, critical stress, and dissipated energy evaluated from the stress-strain curves decrease bymore » about a half with increasing the temperature, whereas there was no drastic changes even around the spin-state transition temperatures. The initial modulus agrees with the temperature dependence of the apparent Young's modulus measured under low-stress cyclic loading.« less
  • Variable-temperature Co-K-EXAFS measurements establish the occurrence of two cobalt sites, probably associated with the two spin states, above 400 K. The population of the two Co sites becomes equal around 670 K, at which temperature the change in space group occurs.
  • LaCoO{sub 3} displays two broad anomalies in the DC magnetic susceptibility {chi}{sup DC}, occurring, respectively, around 50 K and 500 K. We have investigated the first of them within the 10 K<T<RT temperature range using Co K{alpha}{sub 1} x-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode. In contrast with previous O K-edge XAS reports, our data show the existence of abrupt changes around 50 K which can be nicely correlated with the anomaly in {chi}{sup DC}. To our knowledge, this is the first time that a clear, quantitative relationship between the temperature dependence of the magnetic susceptibility andmore » that of the XAS spectra is reported. The intensity changes in the preedge region, which are consistent with a transition from a lower to a higher spin state, have been analyzed using a minimal model including the Co 3d and O 2p hybridization in the initial state. The temperature dependence of the Co magnetic moment obtained from the estimated e{sub g} and t{sub 2g} occupations could be satisfactorily reproduced. Also, the decrease of the Co 3d and O 2p hybridization by increasing temperature obtained from this simple model compares favorably with the values estimated from thermal evolution of the crystallographic structure.« less
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