27-30 January 2019
Europe/Prague timezone

Winter School Topics

Title: Key steps  in processing of ferroelectrics: solid state synthesis of the perovskitic phase, cold consolidation and densification

Carmen Galassi

The processing of bulk ferroelectric materials is based on several steps each of them with the potential of limiting the final properties of the materials, if not carefully addressed and  optimized. The solid state synthesis is the most used  method  to produce the  perovskitic phase , and the massively one chosen for the production of the commercial powder.  It is based on the thorough mixing of the starting oxides or carbonates  followed by solid-state reaction (SSR) at high temperatures. The successful production of powders depends on the control of the synthesis parameters and purity and morphology of the  raw materials. The content of the perovskitic phase as well as the morphology and cold compaction behaviour of the powders strongly influence the  behaviour of the powder during densification and the final microstructure of the sintered material. Milling steps introduced after SSR result of outmost importance in order to enhance the  green density of the samples produced either  by  dry pressing or  colloidal processing. The densification step is critical as the difficulty to achieve full density  is associated with the  easy of  evaporation of elements of the composition and stoicheiometry loss. These issues will be addressed with  focus on the  optimization of the conventional and cheap  processing techniques, with main reference to the PZT based compositions.

Title: 'Wet-Chemistry' Routes to Functional-Oxide Thin Films and Nanostructures:  Chemical Solution Deposition and Inkjet Printing

Prof. Barbara Malič

1Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
2Jožef Stefan International Postgraduate School, Jamova cesta 39, 1000 Ljubljana, Slovenia

Solution-derived, or sol-gel, functional-oxide thin films have been extensively studied in the last decades. The drive for research of ferroelectric thin films has been the miniaturization of components in micro-electronics and micro-electro-mechanical systems (MEMS); conductive oxides have found applications in transparent electronics or in various sensors, to name only a few. Solution processing of functional-oxide thin films, also referred to as the Chemical Solution Deposition (CSD), in analogy with Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD) processes, starts with the synthesis of the coating solution or sol. The latter is then deposited on a substrate very often by spin-coating. In the drying and pyrolysis steps the evaporation of residual solvent(s), continued reactions, de-hydroxylation, thermal oxidation of functional groups and usually partial densification occur. The crystallization step is needed to establish the long-range order, for example, in ferroelectrics, but not necessarily in materials for transparent electronics, such as conductive oxides. To pattern structures lift-off lithography is usually employed, and the process includes many steps, and produces waste.

As alternative, inkjet printing is a direct writing technique, in which the material is deposited only where needed. It is a non-contact mask-less method, and the design is made directly in the computer. It needs low amounts of materials, which contributes to reduced waste and cost, and the scalability to large area manufacturing is possible. In piezoelectric inkjet printing the design of the ink needs to take into account the fluid properties that enable formation of uniform drops and result in a deposited pattern which keeps its predetermined shape upon deposition and consequent drying and heating steps.

Title: Elaboration process of piezoelectric ceramic materials

Pascal Marchet

The piezoelectric ceramics represent a subgroup of electroceramics materials. At the present time, they are being used in a wide range of everyday life applications, such as gas lighters, pressure sensors, automotive electronics, car parking sensors, piezoelectric motors, ultrasonic transducers for sonar or medical echography…. The corresponding devices are using either bulk ceramic materials or thick films, or wether thin films.

As for all polycristalline materials, the final properties, i.e. in our case the piezoelectric properties, are a combination of intrinsic and extrinsic properties. Therefore, this properties widely depends on the elaboration process. Thus the aim of the presentation will be to review and explain the elaboration processes for piezoelectric materials. The methods of synthesis and sintering of ceramics and thick/thin films will be emphasized and correlated to the properties of the materials. 

Title: Piezoelectric, elastic and dielectric characterization of  ferro-piezoelectric ceramics, including all losses: 25 years of use of the automatic iterative analysis of impedance curves at resonance

Lorena Pardo

Instituto de Ciencia de Materiales de Madrid (ICMM).CSIC. Sor Juana Inés de la Cruz, 3. Cantoblanco. 28049-Madrid, Spain

Since the first IRE Standards for measurements were issued in 1961, the resonance method for characterization of piezoelectric ceramics from impedance measurements at the electromechanical resonances of poled ceramic resonators became widely extended. The next generation of Standards (IEEE, 1987) are worldwide used nowadays, though at revision at present [1]. For each mono-modal resonance of a given geometry resonator a set of piezoelectric, dielectric and elastic parameters in the linear range can be obtained, including all losses [2]. For the full characterization of poled piezoceramics, thus with an axial macroscopic symmetry, a set of ten independent parameters must be determined (3 piezoelectric, 5 elastic and 2 dielectric), which requires using 3 resonator geometries and 4 resonance modes. In the 1990s a number of alternative to Standard methods of analysis of the complex impedance curves at resonance were issued. Some of these deal with all material losses by determining parameters in complex way. 25 years of in-operando characterization of ferro-piezoelectric ceramics, including elastic, dielectric and piezoelectric losses will be presented [3-4]. 

[1] “Publication  and  proposed  revision  of ANSI/IEEE  standard  176-1987”. IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 43, 717 (1996)
[2] A. M. González, Á. García, C. Benavente-Peces and L. Pardo “Revisiting the Characterization of the Losses in Piezoelectric Materials from Impedance Spectroscopy at Resonance” Materials, 9(2), 72 (2016)
[3] C. Alemany, L. Pardo, B. Jiménez, F. Carmona, J. Mendiola and A.M. González. “Automatic iterative evaluation of complex material constants in piezoelectric ceramics". J. Phys. D: Appl. Phys., 27, 148 (1994)
[4] http://icmm.csic.es/gf2/medidas.htm