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Title: A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth)

Abstract

A comparative study of the magnetic properties of a few members of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} family with different radii of the A-site cations, <r{sub A} >, in the range 1.19-1.40 A has been carried out. The apparent T {sub c} (where the magnetization undergoes an abrupt increase) decreases markedly with <r{sub A} > as well as the size-disorder arising from the mismatch in the size of the A-site cations. The value of the magnetization at low temperatures decreases markedly with decrease in <r{sub A} > or increase in size-disorder, suggesting that the relative proportion of the ferromagnetic (FM) species decreases relative to that of the paramagnetic (PM) species. Such a variation of the FM/PM ratio with composition and temperature is evidenced from the Moessbauer spectra of La{sub 0.5}Sr{sub 0.5}CoO{sub 3} as well. The variation of the FM/PM ratio with <r{sub A} > and size-disorder, as well as a local-probe study using {sup 59}Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with <r{sub A} > and size disorder. - Graphicalmore » abstract: Variation of (a) T {sub c} and (b) FC magnetization at 1000 Oe with <r{sub A} > at 120 K in Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} and Dy{sub 0.34}Nd{sub 0.16}Sr{sub 0.40}Ca{sub 0.10}CoO{sub 3}.« less

Authors:
 [1];  [2];  [2];  [2];  [3]
  1. Chemistry and Physics of Materials Unit and CSIR Centre of Excellence in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064 (India)
  2. Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India)
  3. Chemistry and Physics of Materials Unit and CSIR Centre of Excellence in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064 (India), E-mail: cnrrao@jncasr.ac.in
Publication Date:
OSTI Identifier:
21015779
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 4; Other Information: DOI: 10.1016/j.jssc.2007.02.003; PII: S0022-4596(07)00076-X; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COBALT COMPOUNDS; MAGNETIC PROPERTIES; MAGNETIZATION; MOESSBAUER EFFECT; NUCLEAR MAGNETIC RESONANCE; OXIDES; PARAMAGNETISM; RARE EARTH COMPOUNDS; SPECTROSCOPY; STRONTIUM COMPOUNDS; TEMPERATURE RANGE 0065-0273 K

Citation Formats

Kundu, Asish, Sarkar, R., Pahari, B., Ghoshray, A., and Rao, C.N.R. A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth). United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.02.003.
Kundu, Asish, Sarkar, R., Pahari, B., Ghoshray, A., & Rao, C.N.R. A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth). United States. doi:10.1016/j.jssc.2007.02.003.
Kundu, Asish, Sarkar, R., Pahari, B., Ghoshray, A., and Rao, C.N.R. Sun . "A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth)". United States. doi:10.1016/j.jssc.2007.02.003.
@article{osti_21015779,
title = {A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth)},
author = {Kundu, Asish and Sarkar, R. and Pahari, B. and Ghoshray, A. and Rao, C.N.R.},
abstractNote = {A comparative study of the magnetic properties of a few members of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} family with different radii of the A-site cations, <r{sub A} >, in the range 1.19-1.40 A has been carried out. The apparent T {sub c} (where the magnetization undergoes an abrupt increase) decreases markedly with <r{sub A} > as well as the size-disorder arising from the mismatch in the size of the A-site cations. The value of the magnetization at low temperatures decreases markedly with decrease in <r{sub A} > or increase in size-disorder, suggesting that the relative proportion of the ferromagnetic (FM) species decreases relative to that of the paramagnetic (PM) species. Such a variation of the FM/PM ratio with composition and temperature is evidenced from the Moessbauer spectra of La{sub 0.5}Sr{sub 0.5}CoO{sub 3} as well. The variation of the FM/PM ratio with <r{sub A} > and size-disorder, as well as a local-probe study using {sup 59}Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with <r{sub A} > and size disorder. - Graphical abstract: Variation of (a) T {sub c} and (b) FC magnetization at 1000 Oe with <r{sub A} > at 120 K in Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} and Dy{sub 0.34}Nd{sub 0.16}Sr{sub 0.40}Ca{sub 0.10}CoO{sub 3}.},
doi = {10.1016/j.jssc.2007.02.003},
journal = {Journal of Solid State Chemistry},
number = 4,
volume = 180,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The ab-initio (GGA+U) electronic structure calculations of layered cobaltates Ln{sub 0.3}CoO{sub 2} (Ln = La, Pr, Nd) prepared by ionic exchange from Na{sub 0.90}CoO{sub 2} precursors have been performed. The data are used for numerical modeling of Seebeck coefficient within Boltzmann transport theory using BoltzTraP program [G. K. H. Madsen and D. J. Singh, Comput. Phys. Commun. 175, 67 (2006)], as well as for determination of the crystal field split levels of rare-earth ions using a method based on a transformation of Bloch states into the basis of Wannier functions [P. Novák et al., Phys. Rev. B 87, 205139 (2013)]. An overallmore » agreement with observed magnetism and transport properties is obtained. In particular, the high p-type thermopower is well reproduced in a broad temperature range, but instead of theoretical linear decrease down to the lowest temperatures, the real systems exhibit an anomalous change of Seebeck sign, which might be related to the change of bare metallic carriers into the polaronic ones.« less
  • A combination of electron, synchrotron X-ray and neutron powder diffraction reveals a new orthorhombic structure type within the Sr-doped rare earth perovskite cobaltates Ln{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (Ln=Y{sup 3+}, Dy{sup 3+}, Ho{sup 3+}, Er{sup 3+}, Tm{sup 3+}and Yb{sup 3+}). Electron diffraction shows a C-centred cell based on a 2{radical}2a{sub p}x4a{sub p}x4{radical}2a{sub p} superstructure of the basic perovskite unit. Not all of these very weak satellite reflections are evident in the synchrotron X-ray and neutron powder diffraction data and the average structure of each member of this series could only be refined based on Cmma symmetry and a 2{radical}2a{sub p}x4a{sub p}x2{radical}2a{submore » p} cell. The nature of structural and magnetic ordering in these phases relies on both oxygen vacancy and cation distribution. A small range of solid solution exists where this orthorhombic structure type is observed, centred roughly around the compositions Ln{sub 0.2}Sr{sub 0.8}CoO{sub 3-{delta}}. In the case of Yb{sup 3+} the pure orthorhombic phase was only observed for 0.850{<=}x{<=}0.875. Tetragonal (I4/mmm; 2a{sub p}x2a{sub p}x4a{sub p}) superstructures were observed for compositions having higher or lower Sr-doping levels, or for compounds with rare earth ions larger than Dy{sup 3+}. These orthorhombic phases show mixed valence (3+/4+) cobalt oxidation states between 3.2+ and 3.3+. DC magnetic susceptibility measurements show an additional magnetic transition for these orthorhombic phases compared to the associated tetragonal compounds with critical temperatures > 330 K. - Graphical abstract: A study using electron, high-resolution synchrotron X-ray and neutron powder diffraction reveals a new family of orthorhombic perovskite superstructures (Ln{sub 0.2}Sr{sub 0.8}CoO{sub 3-{delta}}), that shows A-site (Ln{sup 3+}/Sr{sup 2+}) cation ordering as well as oxygen vacancy ordering.« less
  • A family of Sr-doped perovskite compounds Ln{sub 1-x}Sr {sub x}CoO{sub 3-{delta}} (Ln = La{sup 3+}, Pr{sup 3+} and Nd{sup 3+}; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 deg. C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm{sup 3+} and an upper limit of Sr{sup 2+} solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancymore » ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln{sup 3+}/Sr{sup 2+} cation ordering was observed.« less
  • The (1-x)(K{sub 0.5}Na{sub 0.5})NbO{sub 3}-x(Ba{sub 0.5}Sr{sub 0.5})TiO{sub 3} (KNN-BST) solid solution has been synthesized by conventional solid-state sintering in order to search for the new lead-free relaxor ferroelectrics for high temperature applications. The phase structure, dielectric properties, and relaxor behavior of the (1-x)KNN-xBST solid solution are systematically investigated. The phase structure of the (1-x)KNN-xBST solid solution gradually changes from pure perovskite phase with an orthorhombic symmetry to the tetragonal symmetry, then to the pseudocubic phase, and to the cubic phase with increasing addition of BST. The 0.90KNN-0.10BST solid solution shows a broad dielectric peak with permittivity maximum near 2500 andmore » low dielectric loss (<4%) in the temperature range of 100-250 deg. C. The result indicates that this material may have great potential for a variety of high temperature applications. The diffuse phase transition and the temperature of the maximum dielectric permittivity shifting toward higher temperature with increasing frequency, which are two typical characteristics for relaxor ferroelectrics, are observed in the (1-x)KNN-xBST solid solution. The dielectric relaxor behavior obeys a modified Curie-Weiss law and a Vogel-Fulcher relationship. The relaxor nature is attributed to the appearance of polar nanoregions owing to the formation of randon fields including local electric fields and elastic fields. These results confirm that the KNN-based relaxor ferroelectrics can be regarded as an alternative direction for the development of high temperature lead-free relaxor ferroelectrics.« less
  • The new compounds Ln{sub 3}TSe{sub 6} (Ln = Sm, Gd; T = In, Cr) and Tb{sub 3}CrSe{sub 6} have been synthesized by the solid-state reactions of the elements at 850 C. A KBr flux was used to promote crystal growth. These isostructural compounds crystallize with the U{sub 3}ScS{sub 6} structure type. The crystal structure is built from LnSe{sub 7} pseudo-octahedra or LnSe{sub 8} bicapped trigonal prisms and TSe{sub 6} octahedra. Magnetic measurements show that Sm{sub 3}TSe{sub 6} (T = In, Cr) and Tb{sub 3}CrSe{sub 6} are paramagnetic down to 5 K whereas Gd{sub 3}CrSe{sub 6} undergoes an antiferromagnetic transition atmore » 10 K.« less