Peculiarities of the microstructure and properties of thin spherolitic PZT films formed by a two-stage radio-frequency magnetron deposition method

Abstract

The paper presents the results of experimental studies of the microstructure and piezoelectric properties of thin lead zirconate-titanate films characterized by either an island structure of radially radiant spherulites located in a low-temperature pyrochlore matrix or a block single-phase spherulitic structure with different linear block sizes. Changing the size of the blocks within 10-50 µm was achieved by varying the distance from the target to the substrate in the range of 30-70 mm, leading to a change in the heating temperature of the substrate in the radio-frequency magnetron sputtering of a ceramic target during film deposition on a «cold» platinized silicon substrate. The temperature of subsequent annealing for the crystallization of the perovskite phase was 550°C for island films and 580°C for single-phase films. Scanning electron microscopy methods have revealed anomalous dependences of the rotation of the growth axis with the growth of the linear dimensions of spherulites, reaching a value of 1,2 deg/μm, and other microstructural parameters of thin films. The observed phenomena were caused by lateral mechanical stresses arising during the solid-state transformation from the pyrochlore phase to the perovskite phase, accompanied by a change in the density of the films. At tensile stresses of the order of the elastic limit, this led to the appearance of intra-block high-angle boundaries. The behavior of lateral polarization was studied by the method of force microscopy of the piezoelectric response and it was shown that tensile mechanical stresses in spherulites lead to the orientation of the lateral polarization vector in the radial direction.

Keywords

• lead zirconate-titanate thin films
• pyrochlore-perovskite phase transformation
• spherulite microstructure
• piezoresponse force microscopy