El Proyecto cuenta con un presupuesto de 96.800 € y ha sido financiado parcialmente por el Ministerio de Ciencia e Innovación y cofinanciado con fondos FEDER.
El personal participante en este proyecto han sido investigadores y personal en formación del Instituto de Cerámica y Vidrio.
• Marina Villegas Gracia (Investigadora)
• Amador Caballero Cuesta (Investigador)
• Marco Peiteado López (Becario Postdoctoral)
• Teresa Jardiel Rivas (Becaria Postdoctoral)
• Mara Bernardo Sacristán (Becaria Predoctoral)
• María Verde Lozano (Becaria Predoctoral)
The concept of bio-inspired soft solution processing has been proposed in the last years as the sustainable way of processing advanced materials. This concept has superlative benefits like energy saving, simplicity, cost effectiveness and nor or little waste so, in essence, with an eye on the environmentally benign conditions and without leading to the global warming. Inspired by the natural processes and the energy by them required, it basically covers all kind of processes to prepare materials which can be operated under ambient, near ambient or just above the ambient conditions.
Following this approach the present project pursues to develop an eco-friendly processing for the obtaining of modern multifunctional electroceramics, which generally are produced by processing techniques that consume high energy in terms of temperature, pressure, vacuum, as well as expensive/sophisticated equipment and/or multi-step fabrication.
AIM: The project pursues the synthesis and consolidation of electroceramic materials by applying bio-inspired solution processing methods. Depending on the complexity of the involved materials there are two ways to be explored:
i) Direct fabrication of ceramic films from a solution without firing or post-treatment. Nucleation and growth rates of ceramic compounds must be matched with the precipitation rates of the multiple components. Single or double oxides films can be form and crystallized if a chemical driving force exists. Interfacial relations between the substrate and the solute can be activated electrochemically by an applied external electric field or UV radiation.
ii) Low temperature processing from ceramic nanoparticles. For complex new double or triple oxides in which the “one step approach” is not possible, the process will be split into two steps; synthesis of suitable oxide nanoparticles as precursors and subsequent reaction-sintering process at very low temperature activated by pressure (hydrothermal conditions) or an electric field.
THE MATERIALS: The approach described above will be applied to three different types of electroceramic materials. These types are defined by their electric behavior and application, and their composition complexity changes from slightly doped single oxides to complex solid solutions between double oxides. For clarity, the materials are shown grouped by electrical families:
ZINC OXIDE BASED SEMICONDUCTORS: ZnO-based varistor materials are universally used in circuit protection. The development of varistor-like nanopowders that could be dissolved/embedded in a variety of polymeric substrates would be a most relevant achievement allowing new levels of component integration and circuit miniaturization. Transparent conductive oxides have attracted much attention as electrodes for flat panel displays, thin film photovoltaics, dye-sensitized solar cells and organic light emitting diodes. Indium-tin oxide (ITO) is widely used in most applications, but indium is a very expensive, toxic, and highly pollutant material. Aluminium-doped ZnO has shown excellent performance and is a very attractive alternative: achieving ZnO-based contacts to organic semiconductors, based on ZnO adsorption at the polymer surfaces and subsequent reaction and formation of a conductive hybrid, will reduce costs and environmental impact.
LEAD FREE PIEZOELECTRICS: The most relevant piezoelectric ceramic are lead zirconate titanate (PZT)-based compositions. They find extensive applications as sensor materials (or transducers or actuators) in smart structures, medical imaging devices, and MEMS. However nowadays there are two demands on new piezoelectric materials. New piezoelectrics for working in severe environmental conditions (especially high temperature) are needed since PZT working temperature never exceeds 300ºC. Bi-based Aurivillius compounds are still promising candidates, however uncontrolled growth during the heat treatments needed to synthesize and sinter both bulk and film configurations, is still a major drawback. Such a growth increases the electrical conductivity and this is detrimental for the possible piezoelectric response. On the other hand environmental concerns necessitates that the increasing market of piezoceramic sensors and actuators can be delivered with lead-free piezoelectric ceramics. Lead-free piezoceramics whose properties match those of PZT are strongly demanded. Recently, theoretical works have predicted the large ferroelectric polarization and piezoelectricity in the hypothetical perovskite-structure oxides bismuth aluminate (BiAlO3) and bismuth gallate (BiGaO3). BiAlO3 is isotypic with multiferroic perovskite-like BiFeO3 and shares structural characteristics with antiferrodistortive PbZrO3. Therefore, Bi(Al,Ga)O3 system has been proposed as a replacement for the widely used piezoelectric material, Pb(Zr,Ti)O3 (PZT). However, the proposed phases have been synthesized only at high temperature and pressure conditions and up to date no dense single films or bulk samples have been properly obtained to characterize the actual piezoelectric response. The low temperature approach combined with a local relatively high electric field is a promising one to success in obtaining a film suitable for piezoelectric measurements. Actually, no experimental piezoelectric coefficients have been reported in the literature for these materials.
MULTIFERROIC MATERIALS: Multiferroics are materials in which magnetization and polarization can coexist. These materials enable the possibility of the electrical control of magnetic state (or viceversa). They can be the key for new applications still in a research and development state like spintronics. Among the known possibilities to produce a material with a ferroelectric state in a magnetically ordered state, the two following approaches can be considered: (1) Bi3+or Pb2+ (on the A-site) based perovskites with magnetic transition-metal ions on the B-site; (2) ferromagnetic superlattices. Within this approaches, BiFeO3 based materials are among the most promising ones. However, understanding the basic conditions for a synthesis of the single phase is still lacking. Authors repeatedly report problems related to the synthesis of this material, and no direct explanation has been given yet for the persistent appearance of secondary phases. Researchers have suggested different reasons for the appearance of the secondary phases: BiFeO3 described as metastable, off-stoichiometric, having a low peritectic decomposition temperature, or with Bi2O3 evaporation affecting its formation. All these assumptions find their origin in the heat treatment; for instance, the stabilization of sillenite Bi25FeO39 at high temperature has been reported to be critical. Therefore the preparation of stable single phase films of BiFeO3 at low temperature from solutions needs is a promising route.