Hole conductivity in oxygen-excess BaTi1-xCaxO3-x+d

BaTiO3 containing Ca substituted for Ti as an acceptor dopant, with oxygen vacancies for charge compensation and processed in air, is a p-type semiconductor. The hole conductivity is attributed to uptake of a small amount of oxygen which ionises by means of electron transfer from lattice oxide ions, generating O- ions as the source of p-type semiconductivity. Samples heated in high pressure O-2, up to 80 atm, absorb up to twice the amount expected from the oxygen vacancy concentration. This is attributed to incorporation of superoxide, O2-, ions in oxygen vacancies associated with the Ca2+ dopant and is supported by Raman spectroscopy results.