The Electrical Properties of Bismuth Oxide

The conductivity σ and thermo-electric power dE/dT of bismuth oxide is measured over a temperature range of 680° to 150° C., and for variations of oxygen pressures from 76 to 10 -4 cm. Hg. The results above 340°C. and at atmospheric pressure are well represented by the formulae σ= A 1 exp (-α/2 T ) and below 340° C. by σ= A 2 exp (-α/ T ), in which the values of the constants A 1 , A 2 and α are very similar for two different specimens. The variation of σ with oxygen pressure above 500° C. and for pressures down to 1 mm. Hg obeys the formula σ=κ( P o 2 ) ¼ . The thermo-electric power results may be summarized by the equation dE/dT = a + b/T , where a and b are constants, the positive sign of dE/dT indicating that Bi 2 O 3 is a defect semiconductor. The variations of dE/dT with oxygen pressure are small less than 10%, except at pressures less than 10 -3 cm. Hg, when the sign of dE/dT changes at temperatures greater than 550° C. Under these conditions it is suggested that B1 2 O 3 becomes an excess or intrinsic semiconductor. The results are discussed and good agreement is obtained between theory and experiment if it is assumed that normal Wagner and Schottky lattice defects become of importance at low temperatures when the concentration of free electrons is small.