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DOI: 10.1039/A900957D (Paper) Reference Section for: J. Mater. Chem., 1999, 9, 1327-1331

Structure and electrical properties of oxygen-deficient hexagonal BaTiO3

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Derek C. Sinclair, Janet M. S. Skakle, Finlay D. Morrison, Ronald I. Smith and Tim P. Beales

Abstract

Rietveld refinements using neutron diffraction data have been used to determine the crystal structure of a series of oxygen-deficient barium titanate powders, BaTiIV1–xTiIIIxO3–x/2 (0<x<0.30). The powders were prepared by reduction of stoichiometric, tetragonal BaTiO3 in a vacuum furnace at temperatures above 1300[thin space (1/6-em)]°C and under an oxygen partial pressure of 0.1 mbar. The 6H-BaTiO3 hexagonal perovskite structure is retained throughout and partial reduction of TiIV to TiIII is accompanied by the formation of O(1) oxygen vacancies in the h-BaO3 layers which separate pairs of occupied face-sharing octahedra, Ti2O9. There is no evidence of O(2) vacancies associated with corner sharing TiO6 octahedra. The Ti(2)-Ti(2) separation within face sharing dimers increases from 2.690(4) Å for x=0 to 2.7469(30) Å for x=0.30. BaTiO2.85 is a band-gap semiconductor at 300 K with a resistivity of ca. 1 Ω cm and activation energy 0.16 eV. A switch in conduction mechanism to variable range hopping (VRH) of electrons between TiIII and TiIV ions occurs on cooling below 240 K.

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