Sintering of ZnO-Gd2O3 ceramic targets for functional thin films

Abstract

This dissertation has investigated the sintering and the magnetic behaviour of Gd-ZnO bulk samples with different Gd concentrations varying from 0 to 1 at.%. The films were deposited using the pulsed laser deposition technique (PLD). This study set out to determine whether Gd-ZnO thin films displayed ferromagnetic behaviour above room temperature using a SQUID magnetometer. However, a problem occurred during the preparation of the PLD targets containing different Gd concentrations. In fact, since the required density for the PLD targets should be more than 90%, the first sets of targets were not sufficiently dense to be utilized in the PLD deposition. Hence, to solve this problem, dilatometry measurements were conducted on a new series of samples so as to find the optimum sintering temperature in order to obtain fully dense targets. The following conclusions can be drawn from the present study. According to the dilatometry measurements conducted on 8 mm diameter Gd-ZnO pellets at constant heating rate of 5 °C/min, the temperature of densification, T onset, which is set arbitrarily to 0.5% shrinkage, increases when the Gd concentration is increased from 0 to 1 at.%. Moreover, non-isothermal dilatometry measurement with three heating rates of 5, 10, and 20 °C/min were carried out on Gd-ZnO bulk samples so as to calculate the apparent activation energy (Q) using both the master sintering curve (MSC) and Arrhenius plot of the sintering data. The results of the magnetic measurements for Gd-ZnO thin films with different Gd concentrations varying from 0 to 1 at.% indicates diamagnetic characteristics at both 5 and 300K; however, a film containing 1 at.% of Gd indicated a super-paramagnetic-like behaviour at 5 K but a saturated magnetization at 300 K. This superparamagnetic behaviour may originate from the formation of the secondary phases during film deposition. Key words: Gd-ZnO pellets; Sintering behaviour; Arrhenius plot; Master Sintering curve; Magnetic behaviour.