Hydrothermal Synthesis Of SrTiO₃and Applicaton In The Varistors

In this paper, SrTiO₃powders were prepared through a hydrothermal methodwith Sr（NO₃）2and [CH3（CH2）3O]4, then spectrophotometry was used to study thebetter process condition for the reaction’s completion. The electrical properties ofSrTiO₃varistor made by the hydrothermal powders and the reason for their changeswere both studied. The better process condition for the reaction’s completion has beenfound. In this condition, the Sr/Ti molar ratio is1.2while the mineralizerconcentration is2.5mol/L, then the temperature is adjusted to160oC and maintainedfor24h. The range analysis of the orthogonal experiment has been studied, and theinfluence strength of the four factors arranged decreasingly as follows: the mineralizerconcentration, the temperature, the length of the reaction time and the Sr/Ti molarratio.With the increasing of the Sr/Ti molar ratio, the Ti concentration of the reactionfiltrate decreases progressively, the grain size decreases progressively, the regularityof the grain appearance gets worse. With the increasing of the mineralizerconcentration, the Ti concentration of the reaction filtrate decreases progressively andthe diffraction peaks height of SrTiO₃powders increases progressively to the hightestpoint and then decreases, meanwhile the grain size increases progressively and theregularity of the grain appearance gets better. With the increasing of the reactiontemperature, the Ti concentration of the reaction filtrate decreases progressively,meanwhile the grain size increases progressively and the regularity of the grainappearance gets better, however, the regularity would get worse at a high temperature.With the increasing of the reaction time, the Ti concentration of the reaction filtratedecreases progressively, the regularity of the grain appearance gets better and littlediversification can be found for grain size. Varistors prepared from hydrothermalSrTiO₃powders exhibited a high V_1mAof120V and absolutely improved É‘ of8,which are both visibly enhanced compared with varistors prepared by traditional solid-state route. The high varistor voltages V_1mAand nonlinear coefficients É‘ can becontributed to the high powder activity of hydrothermal SrTiO₃, which makes themmerge and grow more easily to form big grains. For varistors with bigger grain size,the grain boundary is longer in the depth direction and O₂penetrated along the grainboundary meeting few barriers than those with smaller grain size when they weresintered in the air, which brought higher O₂concentration in grain boundaries. O₂withhigh electronegativity can capture free electrons from the lattice surface, so that theinterface state density increases, resulting in increased grain boundary barrier heightand varistor property. As a result, higher O₂concentration in grain boundaries bringsbetter varistor property. The electrical properties examination and XRF results showthat the little addition of alkali metal ions in the hydrothermal reaction contributeslittle to the enhancement of the varistors’ electrical properties.