Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La2-zCo1+y(MgxNb1-x)1-yO6 double perovskites
Artikel i vetenskaplig tidskrift, 2015

New La-deficient double perovskites with P21/n symmetry, La∼1.90(Co2+1-xMg2+x)(Co3+1/3Nb5+2/3)O6 with x=0, 0.13 and 0.33, and La2(Co2+1/2Mg2+1/2) (Co3+1/2Nb5+1/2)O6 were prepared by solid state reaction at 1450 °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 N2 gas atmosphere at 1200 °C ∼1% O atom vacancies are formed together with a partial reduction of the Co3+ content. The average thermal expansion coefficient between 25 and 900 °C of La1.90(Co2+2/3Mg2+1/3)(Co3+1/3Nb5+2/3)O6 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 °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 ∼100 times larger conductivities at 600 °C, 0.35 and 1.0 S cm-1, respectively, and lower activation energies, 0.57 and 0.73 eV, respectively.

Double perovskite

Crystal structure

Conductivity

Neutron powder diffraction

A-cation deficiency

Författare

Samrand Shafeie

Chalmers, Material- och tillverkningsteknik, Yt- och mikrostrukturteknik

B. Dreyer

Stockholms universitet

R.H.P. Awater

Stockholms universitet

T. Golod

AlbaNova University Center

J. Grins

Stockholms universitet

J. J. Biendicho

ISIS Facility

Stockholms universitet

S. Y. Istomin

Moscow State University

G. Svensson

Stockholms universitet

Journal of Solid State Chemistry

0022-4596 (ISSN) 1095-726X (eISSN)

Vol. 229 243-251

Ämneskategorier

Nanoteknik

DOI

10.1016/j.jssc.2015.06.009