NONSTOICHIOMETRY OF THE TERBIUM OXIDE

The x values of nonstoichiometric chemical formula, Tb4O7-delta or TbO 1.5+x, have been determined in temperature range from 600-degrees-C to 1000-degrees-C under oxygen partial pressure of 2 X 10(-5) to 1 X 10( -5) atm by using quartz microbalance. The x values varied from 0.0478 to 0.1964 in the above conditions. The enthalpy of formation for x' in TbO1.5+(0.25-xo-x'), DELTAH(f), was 4.93-3.40 kcal mol-1 and the oxyg en partial pressure dependence was -1/8.80 approximately -1/11.8 under these conditions. The electrical conductivity of the TbO1.5+x was mea sured under the same conditions and the values varied from about 10(-3 ) to 10-(6) OMEGA-1cm-1 within semiconductor range. The activation ene rgies for the conduction increase with oxygen partial pressure from 0. 83 to 0.89 eV under the above conditions. The 1/n values obtained from the oxygen pressure dependence of the conductivity are 1/4.4-1/5.2. T he conduction mechanism, defect structure, and other physical properti es of the oxides are dicussed with the x values, the electrical conduc tivity values, and the thermodynamic data.