Role of the microstructure in the neutron and gamma-ray irradiation stability of solution-derived Ba0.5Sr0.5TiO3 thin films

The influence of neutron and gamma-ray irradiation on the kilohertz- and microwave-range dielectric properties of polycrystalline Ba0.5Sr0.5TiO3 thin films was investigated. The solution-derived films were prepared on polycrystalline alumina substrates and their microstructures were controlled through the deposition procedure and the annealing temperature. The approximately 600 nm-thick films were either quite porous, consisting of fine, ∼35 nm equiaxed grains, or dense, with predominantly columnar grains with an in-plane size of ∼100 nm. Much thinner, ∼170 nm-thick films with a dense columnar microstructure, and an approximately 70 nm in-plane grain size were also prepared. The irradiation doses were 1.1 × 1014 n cm−2 and 167 kGy for the neutrons and gamma rays, respectively. No microstructural changes were observed in the films. However, the film with the granular microstructure showed much reduced microwave dielectric properties after the neutron irradiation. The films with the columnar microstructure are less sensitive to both types of irradiation, with the thicker films showing decreased values of the extrinsic dielectric losses. The effect is discussed in terms of the influence of microstructural features, such as grain boundaries, pores and microcracks, as well as crystal-lattice defects on the irradiation-damage accumulation rate, concluding that the microstructure of the pristine films is decisive for the irradiation hardness of ferroelectric thin films used for microwave applications.