I. P. Pronin

Peculiarities of phase transitions in sodium-bismuth titanate

Abstract The ferroelectric properties of (Na0,5Bi0,5TiO3) single crystals are studied. It is found that some physical characteristics possess a large temperature hysteresis in the temperature range 200 – 300°C. The nature of that hysteresis is discussed.

Crystallization of thin polycrystalline PZT films on Si/SiO2/Pt substrates

This paper reports on a study of crystallization of thin lead zirconate-titanate films deposited on Si/SiO2/Pt substrates by RF magnetron sputtering at a low temperature and annealed at 540–580°C. In this temperature interval, one observes successively two first-order phase transitions: the low-temperature pyrochlore phase—perovskite-I phase and perovskite-I phase-perovskite-II phase transitions, which are accompanied by film volume shrinkage. The phase transformations have been studied by atomic force microscopy, scanning electron microscopy, X-ray diffraction and visual (optical) observation of the growth of islands of a new phase. It has been found that the dielectric parameters undergo substantial changes upon the transition from phase I to phase II. The origin of the observed effects has been discussed.

Formation and relaxation mechanisms of the self-polarization in thin ferroelectric films

The nature and mechanisms of formation of the spontaneous polarization arising in thin ferroelectric films in the course of formation of a thin-film capacitor structure and relaxation of this polarization under the action of an electric field, temperature, and illumination are discussed.

Epitaxial heterostructures YBa2Cu3O7−δ/KTaO3 for microwave applications

Combinations of high TC superconducting and ferroelectric films may give rise to tunable, high‐Q microwave components. c‐axis oriented YBa2Cu3O7−δ films were grown by laser ablation on (001) and vicinically cut KTaO3 substrates and studied by x‐ray diffraction and electron microscopy. Competitive superconducting properties were registered. YBa2Cu3O7−δ/KTaO3/YBa2Cu3O7−δ trilayers were deposited on silicon‐on‐sapphire buffered by CeO2/Y‐ZrO2. The dielectric permittivity of KTO3 at 15–100 K decreased considerably when the layer was polarized by a dc voltage. A loss factor tan δ=0.007 was measured at 100 kHz and T=50–100 K.

Anomalous losses of lead in crystallization of the perovskite phase in thin PZT films

A study has been performed of the mechanisms underlying evolvement of excess lead oxide from lead zirconate titanate films grown ex-situ in two different regimes by magnetron sputtering. In the first case, crystallization of the dense phase of perovskite passed through an intermediate “porous” phase, and in the second, straight through. It has been found that the anomalously large losses of lead are caused by migration of lead over interphase porous boundaries to the surface of the films and depend strongly on the regime of film preparation. The unusual variation of film composition with increasing annealing temperature has been discussed.

Peculiarities of crystallization of thin ferroelectric films of lead zirconate titanate

The thermodynamics of processes involved in the growth and annealing of ferroelectric films of lead zirconate titanate Pb(Ti,Zr)O3 (PZT) has been studied using the method of synchronous thermal analysis (STA). Thin PZT films were grown by the RF magnetron sputtering and then annealed in air or in an inert gas (argon) at atmospheric pressure and various temperatures within 20–600°C. It was found that the annealing in an oxygen-containing medium (air) is accompanied by changes in the enthalpy and mass of the system, which is due to the interaction with oxygen, while the heat treatment in an inert medium did not lead to any changes in the PZT film. It is established that the observed changes are related to the conversion of lead monoxide into orthoplumbate in the PZT film volume. STA experiments demonstrate that this transformation leads to a significant change in the structure of the ferroelectric film. Based on these data, a mechanism is proposed that accounts for the structural changes involved in the annealing of PZT films.

Self-polarization and migratory polarization in thin lead zirconate-titanate films

This paper reports on a study of the electrical properties of 0.7–1-µm-thick textured PZT ferroelectric films prepared by rf magnetron sputtering of a PbZr0.54Ti0.46O3 target which additionally contained 10 mol % lead oxide. Such films are shown to feature a combination of a self-polarized state and migratory polarization. The totality of the data obtained suggest that the films had n-type conduction. As shown by the laser beam modulation technique, the polarization was distributed nonuniformly in depth, with most of the poled state localized near the lower interface of the thin-film ferroelectric capacitor. The mechanism underlying the onset of this self-polarization is related to the charging of the lower interface of the structure by electrons, which occurs during the cooling following the high-temperature treatment of the PZT film, and to poling of the bulk of the film by the charged interface. This mechanism of the self-polarization of ferroelectric films is believed to have a universal character.

Specific properties of the PZT-based thin-film capacitor structures with excess lead oxide

The effect of excess lead oxide on the microstructure and ferroelectric properties of lead zirconate titanate (PZT) films was studied in PZT-based thin-film capacitor structures. It is shown that excess lead in the form of lead oxide is localized at the grain boundaries and film-platinum electrode interfaces, which can result in the appearance of internal electric fields and the self-polarization of PZT films. It is suggested that the selfpolarization effect is related to the formation of a built-in electric charge with different densities at the bottom and top metal electrode-ferroelectric film interfaces.

Pyroelectric and piezoelectric properties of thin PZT films at the morphotropic phase boundary

It has been shown that, in polycrystalline thin PZT films with the Zr/Ti = 0.535/0.465 ratio of ions in octahedral positions of the perovskite structure, the permittivity and the pyroelectric and piezoelectric responses increase with increasing linear sizes of growth blocks to reach anomalously large values. It has been assumed that the observed effects originate from a combination of two factors, namely, the possible presence of the monoclinic phase and a well-developed domain structure in the films.

Mechanism of the phase transformation of the pyrochlore phase into the perovskite phase in lead zirconate titanate films on silicon substrates

The phase transformation from the pyrochlore phase into the perovskite phase in ferroelectric films of lead zirconate titanate on silicon substrates due to annealing of samples has been investigated experimentally and theoretically. It has been proved that this transformation is a typical first-order phase transition, which is accompanied by a change in the density of the phases and the release of the latent heat of the phase transition. The quantitative evaluations have demonstrated that the difference in the densities of two phases, namely, the perovskite phase and the original parent pyrochlore phase, leads to the generation of elastic stresses in the original parent phase. In turn, these stresses bring about the nucleation of micropores in the bulk of the lead zirconate titanate film. The thermodynamic conditions providing the formation of micropores have been established and the critical size of the micropores has been calculated. A characteristic relationship between the critical size of nuclei of the perovskite phase and the radius of micropores at which the perovskite phase is separated from the parent pyrochlore phase has been derived. This relationship has been verified experimentally. The sizes of the micropores have been determined using scanning electron microscopy, and the changes in the phase composition during the phase transformation have been found using an electron probe X-ray microanalysis. It has been demonstrated theoretically and experimentally that the relaxation of elastic stresses in the lead zirconate titanate thin films during the phase transition occurs through the nucleation and growth of micropores at the interface between the new and parent phases.