Dielectric relaxation and variable-range-hopping conduction in BaSn1-xCrxO3 system

The possibility of formation of a solid solution in the system BaSn1-x Cr (x) O-3 has been explored upto x <= 0.20. It has been confirmed that single phase solid solution forms upto x <= 0.10. Dielectric and conduction behaviour of single phase samples have been studied in the temperature range 400-610 K and frequency range 10 Hz-2 MHz. Two dielectric relaxation processes in two different frequency ranges have been observed. The temperature dependence of both dc and ac resistivity obey relation rho = rho(o) exp(B/T-1/4), indicative of variable range hopping conduction mechanism. The activation energy for dc conduction is higher than that for relaxation time (tau) of low frequency dielectric relaxation process. It has been observed that activation energy for dielectric relaxation matches with activation energy for ac conductivity (at 100 kHz) for both the dielectric relaxation processes. Seebeck coefficient 'alpha' of the samples have been measured in the temperature range 350-650 K. Negative value of 'alpha' in the entire range of temperature measurement shows that conduction species are negatively charged. On the basis of value of activation energy for dc conduction and sign of Seebeck coefficient, conduction in the low temperature region (below 500 K) is attributed to hopping of weakly bonded electrons among Sn2+ double left right arrow Sn4+ or Sn3+ double left right arrow Sn4+ and that in the high temperature region (above 500 K) to hopping of doubly ionized oxygen vacancies (V-o(circle circle)).