Abstract
The electronic conductivity, σe, Hall constant, R, and thermoelectric power, Θ, in α Ag2Te are measured as the Ag/Te ratio is varied by the use of the galvanic cell Ag|AgI|Ag2Te|Pt, where the e.m.f. of the cell, E, represents the position of the Fermi level relative to Ag-saturated Ag2Te. According as Ag is removed across the cell, starting from the Ag-saturated composition, σe decreases at first, and then increases. Θ changes its sign at the minimum of σe, although R is always n-type, duing to the large mobility ratio (∼100). The energy gap is, therefore, as narrow as several kT. When Ag is removed further, σe decreases again, keeping E constant. This is a mixed state of Ag2Te and a new phase mentioned below. After a minimum of σe is attained, σe and E increase again, suggesting a new phase, Ag∼1.93Te. The energy gap of this phase is fairly larger than that in Ag2Te phase and the mobilities of electron and hole are far smaller than those in Ag2Te. When Ag is removed still further, σe and E become to be independent of the composition, indicating the precipitation of Te or Te rich compound. Those experimental data are compared with the Lorentz-Sommerfeld theory, proving a good accordance between them. On the other hand, ionic conductivity is estimated from the ionic polarization effect.
