Registro de acceso restringido Este recurso no está disponible en acceso abierto por política de la editorial. No obstante, se puede acceder al texto completo desde la Universitat Jaume I o si el usuario cuenta con suscripción. Registre d'accés restringit Aquest recurs no està disponible en accés obert per política de l'editorial. No obstant això, es pot accedir al text complet des de la Universitat Jaume I o si l'usuari compta amb subscripció. Restricted access item This item isn't open access because of publisher's policy. The full--text version is only available from Jaume I University or if the user has a running suscription to the publisher's contents.
The electrical properties of Ca-doped BaTiO3 are very different when Ca substitutes onto Ba or Ti sites. The p-type semiconductivity of Ti-substituted ceramics increases reversibly by one to two orders of magnitude under a dc-bias voltage of ≤100 V cm−1, whereas Ba-substituted ceramics show little sensitivity to a dc bias. This increase in BaTi1−xCaxO3−x, studied over the temperature range 150–600 °C, is independent of electrode material and atmosphere and is attributed to ionization of underbonded O2− ions adjacent to acceptor-doped Ca2+ ions.
Registro de acceso restringido Este recurso no está disponible en acceso abierto por política de la editorial. No obstante, se puede acceder al texto completo desde la Universitat Jaume I o si el usuario cuenta con suscripción. Registre d'accés restringit Aquest recurs no està disponible en accés obert per política de l'editorial. No obstant això, es pot accedir al text complet des de la Universitat Jaume I o si l'usuari compta amb subscripció. Restricted access item This item isn't open access because of publisher's policy. The full--text version is only available from Jaume I University or if the user has a running suscription to the publisher's contents.
Single phase ceramics of composition Sr(Ti1–xMgx)O3–x: 0 ≤ x ≤ 0.01 were prepared by sol–gel synthesis and characterized by X‐ray diffraction, scanning electron microscopy, impedance spectroscopy, and current–voltage measurements. The bulk and grain‐boundary conductivities increase on application of a small dc bias voltage in the range 3–200 V/cm and at temperatures in the range 150°C–800°C. A qualitatively similar increase in conductivity occurs on increasingPnormalO2 in the surrounding atmosphere, which shows that conduction is p type. The conductivity increase is reversible on removal of the dc bias or on reducing PnormalO2 and is not observed in undoped SrTiO3. It is an intrinsic property of the bulk material, differs from the voltage‐dependent effects observed with varistors and is attributed to changes in redox equilibria between oxygen species at the surface which cause changes in carrier concentration in the interior. A capacitive model of this low‐field dc bias effect is presented and compared with a memristive model of high field resistance degradation.
The electrical conductivity of both BaO-deficient and TiO 2 -deficient BaTiO 3 ceramics shows nonohmic, low field characteristics at temperatures > ~ 200 o C in contrast to stoichiometric BaTiO 3 for which the electrical conductivity is independent of applied voltage. The non-linearity is observed in both bulk and grain boundary resistances of ceramics that are both porous (~82%) and non-porous (~98%) and is not associated with interfacial phenomena such as Schottky barriers and memristors nor with charge injection from the electrodes. Results, shown as a function of time over the temperature range 200 to 750 °C with field gradients in the range ~ 0.5 to 20 Vmm -1 , indicate that an excited state is reached that is time-, temperature-and field-dependent. This effect appears to be caused by departures from local electroneutrality in the defect structure of non-stoichiometric BaTiO 3 which are reduced by electron transfer on application of a dc bias, leading to a more conducting, low-level excited state in which holes associated with underbonded oxygens, presumably as O -ions, are the principal charge carriers. Ceramics gradually return to their ground state in two stages on removal of the dc bias and the conductivity decreases overall by 2-3 orders of magnitude. IntroductionThe electrical properties of resistive materials in bulk form generally show linear voltage-current, V-I, behaviour at small applied voltages although at high voltages, insulating materials exhibit dielectric breakdown. 1 For materials in which conduction takes place by a hopping mechanism, of either ions or electrons, the conductivity can be modelled using random walk theory 2 and the effect of a small dc voltage is simply to apply a slight bias to the random motion of the conducting species, leading to a net drift in a particular direction. A small dc bias is insufficient to force ions or electrons to move; consequently, the V/I response obeys Ohm's Law.In contrast to bulk properties which obey Ohm's Law, non-linear characteristics are commonly associated with interfacial effects, such as electrode-sample contacts which give rise to Schottky barriers. 1 There is also current interest in memristor effects in which, for the specific case of TiO 2 / TiO 2- interfaces, coupled electronic and ionic charge transfer occurs across the interface giving rise to non-linear phenomena. 3 We have recently reported three examples of hopping electronic conduction in bulk ceramics of acceptor-doped BaTiO 3 (BT) that exhibit non-linear characteristics at low field and at temperatures in the range 140 to 650 ºC. [4][5][6] The dopants were Zn 2+ , Mg 2+ and Ca 2+ which substituted for Ti 4+ in the octahedral sites of the perovskite structure, with concentrations in the range 0.003 to 3 mole%.Both bulk and grain boundary conductivities increased by 1 to 2 orders of magnitude, at a rate that was dependent on temperature, on applying a dc bias in the range ~ 0.5 to 20 Vmm -1 at the same time as the ac impedance measurements were made. On removal of th...
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