ac Hall Measurements in Crystals of Strontium Titanate from 190 to 500°K: Dependence of Hall Mobility on Charge-Carrier Density

Results of ac Hall mobility measurements in crystals of strontium titanate in different stages of reduction are reported for the temperature range 190-500°K. The charge-carrier concentration of one of these crystals was two orders of magnitude less than for crystals measured in any previously reported work. A dependence of the magnitude of the mobility on the density of charge carriers was found, with the mobility increasing with an increase in the degree of reduction of the crystals. The temperature variation of the mobility is essentially the same for all the samples, and assumes the form ${\mu }_0{e}^{\frac{\Theta }{T}}$, with ${\mu }_0$ and $\Theta$ constants. A value for $\Theta$ about 700°K was calculated from the data, and values for ${\mu }_0$ were 0.42, 1.0, and 1.42 ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$, with the lowest value corresponding to the sample with least reduction. A polaron mass was calculated using the value of ${\mu }_0$ for the least-reduced crystal, and was found to be $3.1m_0$, with $m_0$ the free-electron mass.