Influence of Jahn-Teller active Mn3+ ions on electrical and dielectric properties, thermopower and Mossbauer spectra of rutile-type Fe1-xMnxNbTiO6 (0 ≤ x ≤ 0.9)

Various electrical and dielectric properties were measured on rutile-type compositions Fe1-xMnxNbTiO6 (0 <= x <= 0.9) between approximate to 100 K and 750 K using impedance spectroscopy. DC conductivity sigma(DC) shows Arrhenius behavior for the bulk above room temperature (RT) for all x values. Starting from x = 0, there is a considerable change in activation energy E-A and sigma(DC)(300 K) between x = 0.1 and 0.2 with increase from E-A approximate to 0.3-0.6 eV, accompanied by a fall in sigma(DC) (300 K) from approximate to 10(-4) to 10(-8)ohm(-l) cm(-1); for x > 0.2 no considerable further variation with rising x is established. For x <= 0.1, below RT Mott's variable range hopping T-1/4 law is obeyed for up sigma(DC). The known relaxor-type behavior of the dielectric constant epsilon' for x = 0 with very high peaks at 500-600 K for low frequencies (163 Hz-6 kHz) changes with rising x to consecutively lower values in epsilon' with disappearance of the peaks and with the largest values at the highest applied temperatures; the relaxor-type behavior can originate from a combination of bulk, grain boundary and sample-electrode effects. Below RT, a dramatic decrease in epsilon' is noted for low x values, resulting finally at approximate to 100 K for compositions of x in the bulk value of epsilon' < 15. The thermopower above RT is negative, hence n-type conduction occurs and charge transport is attributed to small polaron hopping. Fe-57 Mossbauer parameters exhibit some irregularities between x = 0.05 and 0.2, ascribed predominantly to the influence of local distortions by Jahn-Teller active Mn3+ ions.