THE DEFECT STRUCTURE OF SRTI1-XFEXO3-Y (X=0-0.8) INVESTIGATED BY ELECTRICAL-CONDUCTIVITY MEASUREMENTS AND ELECTRON-ENERGY-LOSS SPECTROSCOPY(EELS)

The electrical properties and defect structure of selected composition s in the SrTi1-xFexO3-y system (x = 0-0.8) have been studied using van der Pauw 4-point conductivity measurements and electron energy loss s pectroscopy (EELS). Using X-ray powder diffraction and selected area e lectron diffraction (SAD), the basic crystal structure was determined to be cubic perovskite for all the investigated compositions. A supers tructure cell 2.2.1 times the ordinary perovskite cell was found in ma terials with x = 0.6 and x = 0.8. The conductivity was measured on sin tered tablets as a function of the partial pressure of oxygen (pO(2) = 10(-25) to 1 atm) at 600-1100 degrees C. The materials investigated a re predominantly p-type electronic conductors at high, n-type conducto rs at low, and ionic conductors at intermediate oxygen partial pressur es. All conductivity contributions increase with increasing iron conte nt. This can be attributed to the acceptor role of the iron, decreased band gap and decreased activation energy for oxygen vacancy migration . The EELS spectra show a shoulder below the oxygen K-edge, increasing in magnitude with increasing iron content and oxygen partial pressure . This shoulder is assigned to empty electron energy states at some of the oxygen atoms, indicating that electron holes are associated with lattice oxygen in the structure. Spectra from the Fe L-edge showed sma ll changes, suggesting that there are few or no empty states at the ir on atoms. (C) 1997 Elsevier Science Ltd.