Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La2-zCo1+y(MgxNb1-x)(1-y)O-6 double perovskites
Number of Authors: 8
2015 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 229, 243-251 p.Article in journal (Refereed) Published
New La-deficient double perovskites with P2(1)/n symmetry, La-similar to 1.90(Co1-x2+Mgx2+)(Co1/33+Nb2/35+)O-6 with x=0, 0.13 and 0.33, and La-2(Co1/22+Mg1/22+) (Co1/23+Nb1/25+)O-6 were prepared by solid state reaction at 1450 degrees C. Their crystal structures were refined using time-of-flight neutron powder diffraction data. Our results show that certain cations such as Nb5+, with very strong B-O bonds in the perovskite structure, can induce A-site vacancies in double perovskites. Upon heating in N-2 gas atmosphere at 1200 degrees C similar to 1% O atom vacancies are formed together with a partial reduction of the Co3+ content. The average thermal expansion coefficient between 25 and 900 degrees C of La-1.90(Co2/32+Mg1/32+)(Co1/33+Nb2/35+)O-6 was determined to be 17.4 ppm K-1. Four-point electronic conductivity measurements showed that the compounds are semiconductors, with conductivities varying between 3.7.10(-2) and 7.7.10(-2) S cm(-1) at 600 degrees C and activation energies between 0.77 and 0.81 eV. Partial replacement of La3+ with Sr2+ does not lead to any increase of conductivity, while replacement of Mg2+ with Cu2+ in La1.9CoCu1/3Nb2/3O6 and La1.8CoCu1/2Nb1/2O6 leads to similar to 100 times larger conductivities at 600 degrees C, 0.35 and 1.0 S cm(-1), respectively, and lower activation energies, 0.57 and 0.73 eV, respectively.
Place, publisher, year, edition, pages
2015. Vol. 229, 243-251 p.
Double perovskite, A-cation deficiency, Crystal structure, Neutron powder diffraction, Conductivity
IdentifiersURN: urn:nbn:se:su:diva-120173DOI: 10.1016/j.jssc.2015.06.009ISI: 000358815100031OAI: oai:DiVA.org:su-120173DiVA: diva2:851766