Barbara Malič

EXAFS Study of Amorphous Precursors for Pb(Zr,Ti)O3 Ceramics

In as-hydrolyzed amorphous precursors of Pb(Zr,Ti)O3 (PZT) ceramics with various Zr/Ti ratios prepared from lead acetate and transition metal n-butoxides in parent alcohol medium the local environment of constituent metal atoms has been determined by EXAFS. The local zirconium atom environment in high-Zr precursors consists of distorted octahedra of oxygen atoms with all the bonds made up of Zr–O–Zr links. For low-Zr precursors a smaller distortion of the oxygen octahedra is observed, and two Ti atoms are found in the second shell. The titanium local environment is almost independent of the Zr/Ti ratio, with five oxygen atoms in the first and two titanium atoms in the second shell of neighbors. Lead atoms contain two oxygen atoms in the first coordination shell. Pb–O–M (M = Zr, Ti) links are identified in all precursors: the former at Zr/Ti 75/25 and the latter at lower Zr/Ti ratios. Although a pronounced tendency for the homocondensation of zirconium species is found down to a Zr/Ti 50/50 ratio, heterometallic links (Pb–O–M) are determined in PZT precursors.

PZT thin films prepared from modified zirconium alkoxide

Abstract Selective modification of zirconium alkoxide by acetic acid or acetylacetone was used in solution processing of PZT Pb(Zr, Ti)O3 thin films by 2-methoxyethanol route. EXAFS results clearly show a decrease of Zr-O-Zr links in the acetic acid modified PZT sol implying a more homogeneous constituent metal distribution. No such decrease in comparison to unmodified sol is found in acetylacetone modified PZT. Higher level of homogeneity achieved in modified PZT sols evokes the perovskite crystallization in thin films and decreases the crystallization temperature on (0001) sapphire. On TiO2/Pt/TiO2/Si the modifiers affect the relative orientation of the perovskite phase.

STUDY OF THE LEAD ENVIRONMENT IN LIQUID AND AS-DRIED PRECURSORS OF PZ, PT AND PZT THIN FILMS

The environment of lead and zirconium atoms in liquid and as-dried precursors for PbZrO3 (PZ), PbTiO3 (PT) and Pb1.1Zr0.53Ti0.47O3 (PZT) thin film deposition were analyzed by EXAFS. The sols were prepared by 2-methoxyethanol route with lead acetate and lead oxide as lead sources. Pb—O—M (M = Zr and/or Ti, depending on the sol composition) linkages were determined in all sols. The choice of lead source weakly influences the lead environment, and strongly influences that of zirconium in both PZ and PZT sols. By drying lead oxide based sols the Pb–M correlation is moderately reduced in PZ, PT and is strongly reduced in PZT.

Sol-Gel Processing of PbZrO3 Thin Films

PbZrO3 (PZ) thin films have been prepared by 2-methoxyethanol route from lead oxide or lead acetate and zirconium n-butoxide. The use of lead oxide as lead source and the seeding layer of TiO2 on Pt/TiO2/SiO2/Si substrate facilitate the formation of the perovskite phase.

Ferroelectric Thin Films for Energy Conversion Applications

The chapter attempts to describe the potential of sol-gel derived ferroelectric thin films in energy conversion applications in two fields, namely in cooling by exploiting the electrocaloric effect and in energy harvesting. First, the basics of the sol-gel processing of ferroelectric thin films with the Pb(Zr,Ti)O3 solid solution as the representative material are described. The electrocaloric effect is described as a reversible temperature change in a material under an applied electric field at adiabatic conditions. Sol-gel derived relaxor ferroelectric thin films demonstrate a giant electrocaloric effect and they could be applied for solid-state cooling devices in microelectronics. In energy harvesting, the energy is derived from external sources, captured, stored and used, for example in small autonomous devices. In ferroelectric thin films, the piezoelectric effect, i.e. the generation of an electric charge upon applied stress, is exploited. Due to the miniaturization of electronic components, thin films with lateral dimensions in nanometer to micrometer range are appropriate candidates for future miniature applications related to energy.

Ink-jet Printing of TiO2 Suspensions

A general approach to prepare aqueous suspensions of inorganic particles suitable for ink-jet printing was developed. Titanium dioxide was used as the model material. Stable colloidal suspensions of TiO2 particles in water were prepared by adjusting the pH. The milling conditions were optimized in order to effectively mill the starting micron-sized powder. After 280 min of milling, the particle size was decreased to dmean = 170 nm. The fluid properties of the suspensions, i.e. viscosity and surface tension, were optimized by increasing the solid load of TiO2 powder and by addition of the surfactant triton X-100. Additionally, glycerol was added to the suspensions to control the drying behavior. The patterns of TiO2 were successfully printed on glass substrates.

Lead-Free Ferroelectric Thin Films

Sol-gel-derived ferroelectric thin films, with lead zirconate titanate (Pb(Zr,Ti)O3, PZT) as one of the most widely studied materials, have been investigated for a wide range of applications, including microelectromechanical systems. The research of environment-friendly alternatives to lead-based materials, to a large extent driven by legislation, has been mainly conducted in the domain of bulk ceramics; however, environment-friendly alternatives to lead-based ferroelectric B. Malič (*) • K. Vojisavljević • T. Pečnik Electronic Ceramics Department, Jožef Stefan Institute, Ljubljana, Slovenia e-mail: Barbara.malic@ijs.si; katarina.vojisavljevic@ijs.si; tanja.pecnik@ijs.si A. Kupec Electronic Ceramics Department, Jožef Stefan Institute, Ljubljana, Slovenia Faculty of Mechanical Engineering, Laboratory for Tribology and Interface Nanotechnology, University of Ljubljana, Ljubljana, Slovenia e-mail: alja.kupec@tint.fs.uni-lj.si # Springer International Publishing AG 2016 L. Klein et al. (eds.), Handbook of Sol-Gel Science and Technology, DOI 10.1007/978-3-319-19454-7_19-1 1 thin films have been also studied in recent years. Three most studied groups of lead-free materials include materials based on sodium potassium niobate solid solution ((K0.5Na0.5NbO3), KNN), bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT), and barium titanate – such as barium zirconate titanate–barium calcium titanate solid solution (Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3, BZT-BCT). In the present review, each group is discussed in terms of material properties, sol-gel processing, and thin film crystallization, microstructure, and functional properties.

Low-Temperature Processing

Low-temperature processing incorporates a variety of strategies implemented in chemical solution deposition (CSD) of functional oxide thin films with the aim of decreasing the final heating temperature and thus overcoming the problems related to interaction with the substrate and/or integration into microelectronic elements/devices, or deterioration of thin-film materials. The crystallization temperatures of thin films with different material compositions have been decreased by modification of the precursor solution and the design of the heating profile to ensure a high level of chemical homogeneity already in the liquid state and throughout the processing. In Pb(Zr,Ti)O3 thin films nucleation layers have been successfully implemented to decrease the temperature of perovskite crystallization. Some combined approaches to achieve lower processing temperatures are presented, including hydrothermal reaction, photochemical activation to facilitate the organics thermal decomposition, and laser activation of the as-deposited films. Oxide semiconductors on the other hand can be used as amorphous inorganic films, therefore the focus is on the design of low-temperature decomposable precursors.

Electrocaloric properties of 0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 ceramics

The electrocaloric (EC) effect is a conversion of electrical energy to heat and may be defined as an adiabatic and reversible temperature change that occurs in a polar material upon external electric field. The aim of our work was to prepare 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) ceramics and to study the EC temperature change (ΔT) vs. applied electric field and temperature. For the synthesis of the 0.7PMN-0.3PT bulk ceramics, PbO, MgO, TiO2 and Nb2O5 were used. The homogenized, stoichiometric powder mixtures were mechanochemically activated in a high-energy planetary mill, and milled in an attrition mill in isopropanol. The powder compacts were sintered at 1200 °C for 2 h in double alumina crucibles in the presence of the packing powder. The ceramic was single phase perovskite, with the relative density of 97 % and a uniform microstructure with the median grain size of 1.0 μm ± 0.5 μm. In order to study the EC effect, a high resolution calorimeter was used. The observed magnitudes of the EC effect confirmed the existence of a large EC effect in this material. A characteristic peak of AT as a function of the electric field was observed near the critical point, with the AT of 2.7 K at 90 kV/cm and 430 K.