Crystal structure and electrical conductivity of lanthanum-calcium chromites-titanates La{sub 1-x}Ca{sub x}Cr{sub 1-y}Ti{sub y}O{sub 3-{delta}} (x=0-1, y=0-1)

Journal Article · Fri Oct 01 00:00:00 EDT 2004 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2004.07.007· OSTI ID:20653399

Vashook, V ^[1]; Vasylechko, L ^[2]; Zosel, J ^[3]; Gruner, W ^[4]; Ullmann, H ^[1]; Guth, U ^[1]

---

1. Institute of Physical Chemistry and Electrochemistry, Dresden University of Technology, D-01062 Dresden (Germany)
2. 'Lviv Polytechnic' National University, 79013 Lviv (Ukraine)
3. Kurt-Schwabe Institute for Measuring and Sensor Technology Meinsberg, D-04720 Ziegra-Knobelsdorf (Germany)
4. Leibniz-Institute for Solid State and Materials Research, P.O. Box 270116, D-01171 Dresden (Germany)

Five series of perovskite-type compounds in the system La{sub 1-x}Ca{sub x}Cr{sub 1-y}Ti{sub y}O{sub 3} with the nominal compositions y=0, x=0-0.5; y=0.2, x=0.2-0.8; y=0.5, x=0.5-1.0; y=0.8, x=0.6-1.0 and y=1, x=0.8-1 were synthesized by a ceramic technique in air (final heating 1350{sup o}C). On the basis of the X-ray analysis of the samples with (Ca/Ti)>=1, the phase diagram of the CaTiO{sub 3}-LaCr{sup III}O{sub 3}-CaCr{sup IV}O{sub 3} quasi-ternary system was constructed. Extended solid solution with a wide homogeneity range is formed in the quasi-ternary system CaCr{sup IV}O{sub 3}-CaTiO{sub 3}-LaCr{sup III}O{sub 3}. The solid solution La{sub (1-x'-y)}Ca{sub (x'+y)}Cr{sup IV}{sub x'}Cr{sup III}{sub (1-x'-y)}Ti{sub y}O{sub 3} exists by up to 0.6-0.7mol fractions of CaCr{sup IV}O{sub 3} (x'0.6-0.7) at the experimental conditions. The crystal structure of the compounds is orthorhombic in the space group Pbnm at room temperature. The lattice parameters and the average interatomic distances of the samples within the solid solution ranges decrease uniformly with increasing Ca content. Outside the quasi-ternary system, the nominal compositions La{sub 0.1}Ca{sub 0.9}TiO{sub 3}, La{sub 0.2}Ca{sub 0.8}TiO{sub 3}, La{sub 0.4}Ca{sub 0.6}Cr{sub 0.2}Ti{sub 0.8}O{sub 3} and La{sub 0.3}Ca{sub 0.7}Cr{sub 0.2}Ti{sub 0.8}O{sub 3} in the system La{sub 1-x}Ca{sub x}Cr{sub 1-y}Ti{sub y}O{sub 3} were found as single phases with an orthorhombic structure. In the temperature range between 850 and 1000{sup o}C, the synthesized single-phase compositions are stable at pO{sub 2}=6x10{sup -16}-0.21x10{sup 5}Pa. Oxygen stoichiometry and electrical conductivity of the separate compounds were investigated as functions of temperature and oxygen partial pressure. The chemical stability of these oxides with respect to oxygen release during thermal dissociation decreases with increasing Ca-content. At 900{sup o}C and oxygen partial pressure 1x10{sup -15}-0.21x10{sup 5}Pa, the compounds with x>y (acceptor doped) are p-type semiconductors and those with xy (donor doped) and x=y are n-type semiconductors. The type and level of electrical conductivity are functions of the concentration ratios of cations occupying the B-sites of the perovskite structures: [Cr{sup 3+}]/[Cr{sup 4+}] and [Ti{sup 4+}]/[Ti{sup 3+}]. The maximum electrical conductivity at 900{sup o}C and pO{sub 2}=10{sup -15}Pa was found for the composition La{sub 0.1}Ca{sub 0.9}TiO{sub 3} (near 50S/cm) and in air at 900{sup o}C for La{sub 0.5}Ca{sub 0.5}CrO{sub 3} (close to 100S/cm)

• OSTI ID: 20653399
• Journal Information: Journal of Solid State Chemistry, Vol. 177, Issue 10; Other Information: DOI: 10.1016/j.jssc.2004.07.007; PII: S0022-4596(04)00386-X; Copyright (c) 2004 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CALCIUM COMPOUNDS
CERAMICS
CHROMITES
CHROMIUM IONS
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
INTERATOMIC DISTANCES
LANTHANUM COMPOUNDS
ORTHORHOMBIC LATTICES
OXYGEN
PARTIAL PRESSURE
PEROVSKITE
PHASE DIAGRAMS
SEMICONDUCTOR MATERIALS
SOLID SOLUTIONS
SPACE GROUPS
TEMPERATURE RANGE 0273-0400 K
TITANATES
TITANIUM IONS
X RADIATION