Lattice crossover and mixed valency in the LaCo{sub 1-x}Rh{sub x}O{sub 3} solid solution

Journal Article · Tue Jun 15 00:00:00 EDT 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2010.04.021· OSTI ID:21421527

Li, Jun; Smith, Andrew E ^[1]; Kwong, Kyei-Sing; Powell, Cynthia ^[2]; Sleight, Arthur W ^[1]

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1. Department of Chemistry, Oregon State University, Corvallis, OR 97331-4003 (United States)
2. National Energy Technology Laboratory-Albany, US DOE, Albany, OR 97321 (United States)

The full LaCo{sub 1-x}Rh{sub x}O{sub 3} solid solution was investigated utilizing structural, electrical transport, magnetic, and thermal conductivity characterization. Strong evidence for at least some conversion of Rh{sup 3+}/Co{sup 3+} to Rh{sup 4+}/Co{sup 2+} is found in both structural and electrical transport data. The crystal structure is that of a rhombohedrally distorted perovskite over the range 0.0{<=}x{<=}0.1. The common orthorhombic distortion of the perovskite structure is found over the range 0.2{<=}x{<=}1.0. A crossover of all three orthorhombic cell edges occurs at x=0.5 giving the appearance of a cubic structure, which actually remains orthorhombic. The octahedra in the orthorhombic structure must be distorted for x values less than 0.5, and the observed distortion suggests orbital ordering for Co{sup 2+}. Electrical resistivity measurements as a function of temperature show semiconducting-like regions for all compositions. There is a steady increase in electrical resistivity as the Rh content increases. Large positive thermopower values are generally obtained above 475 K. With increasing Rh substitution there is a decrease in thermal conductivity, which slowly rises with increasing temperature due to increased electrical conductivity. The electronic part of the thermal conductivity is suppressed significantly upon Rh substitution. A thermoelectric figure-of-merit (ZT) of about 0.075 has been achieved for LaCo{sub 0.5}Rh{sub 0.5}O{sub 3} at 775 K, and is expected to reach 0.15 at 1000 K. - Graphical abstract: A complete solid solution is formed between LaCoO{sub 3} and LaRhO{sub 3}. The effect of Rh substitution for Co on the lattice crossover, mixed valency and physical properties is described.

• OSTI ID: 21421527
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 6; Other Information: DOI: 10.1016/j.jssc.2010.04.021; PII: S0022-4596(10)00168-4; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COBALT IONS
COBALT OXIDES
ELECTRIC CONDUCTIVITY
LANTHANUM COMPOUNDS
MAGNETISM
ORTHORHOMBIC LATTICES
PEROVSKITE
RHODIUM IONS
RHODIUM OXIDES
SOLID SOLUTIONS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
THERMAL CONDUCTIVITY
VALENCE
CHALCOGENIDES
CHARGED PARTICLES
COBALT COMPOUNDS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DISPERSIONS
ELECTRICAL PROPERTIES
HOMOGENEOUS MIXTURES
IONS
MINERALS
MIXTURES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PEROVSKITES
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
RHODIUM COMPOUNDS
SOLUTIONS
TEMPERATURE RANGE
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS