A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

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Mechanochemistry: opportunities for new and cleaner synthesis

Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.

http://science.sciencemag.org/content/sci/313/5785/334.full.pdf

A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

The phase transition between the ferroelectric and relaxor states for $0.8\mathrm{Pb}({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}\text{\ensuremath{-}}0.2\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramics with high chemical homogeneity has been studied by measurements of the dielectric and elastic properties as a function of temperature and of thermal expansion. The room temperature ferroelectric phase structure has been studied in ceramics and powdered samples by Rietveld analysis of x-ray diffraction patterns and by ferroelectric hysteresis loops. Results indicate that the material has well defined, different transition and freezing temperatures, such as the transition is between a monoclinic Cm ferroelectric phase and the nonergodic glass state. The transition presents thermal hysteresis, not only in the transition temperature, but in the kinetics. This indicates that a quite sharp slowing down occurs in the temperature interval between 334 and $344\phantom{\rule{0.3em}{0ex}}\mathrm{K}$: the transition temperatures on cooling and heating.

Transition between the ferroelectric and relaxor states in 0.8 Pb ( Mg 1 ∕ 3 Nb 2 ∕ 3 ) O 3 − 0.2 Pb Ti O 3 ceramics

Chemical solution deposition (CSD) methods for ferroelectric thin films make higher reliability and lower processing temperatures feasible. Different reactivities of the constituent transition metal alkoxides may decrease the homogeneity on the molecular level in the ceramic precursors during the synthesis and subsequent processing steps: deposition of the film, drying, consolidation and crystallization of the target ferroelectric phase. In the 2-methoxyethanol based synthesis of Pb(Zr0.53Ti0.47)O3, a selective modification of the reactive Zr alkoxide by acetic acid results in a more homogeneous distribution of constituent metal atoms in the sol as compared to the sol prepared from the as-received Zr-propoxide. The improved chemical homogeneity is reflected in the improved functional response of the films.

Homogeneity issues in chemical solution deposition of Pb(Zr,Ti)O3 thin films

Mechanochemical synthesis of NaNbO3

Direct measurements of the motion of domain walls in disordered ferroelectrics provide important information on their interaction with defects, which is crucial for the functioning of various ferroelectric devices such as high-K capacitors and ferroelectric-based memories In this work, we report on the results of the nanoscale measurements of domain-wall velocity and static domain-wall roughness in disordered (Pb,La)(Zr,Ti)O3 (PLZT) ceramics prepared by hot press sintering Relaxation of domain walls to their equilibrium configurations at short length scales yields the apparent roughness exponent ζ ≈ 067 in PLZT 95/65/35 At the same time, the dynamical exponent μ was found to be about 025 from the independent measurements of domain-wall creep under local application of electric field An analysis of these two values points to the effective dimensionality deff = 1 for the domain walls in PLZT with high La content This result is confirmed by the layer-by-layer polishing followed by the imaging of an a

Quasi-one-dimensional domain walls in ferroelectric ceramics: Evidence from domain dynamics and wall roughness measurements

We have investigated the processing of 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (PMN–PT) thick films on platinised alumina substrates. Nanosized PMN–PT powder with 2 mol% of excess PbO was prepared by high-energy milling and deposited on the substrate using screen-printing technology. The films were then sintered at 950 °C in a PbO-rich atmosphere. The influence of the sintering time and the amount of PbO-containing packing powder was studied and related to the structural, microstructural, dielectric and piezoelectric properties of the film. In order to obtain a homogeneous and dense thick film without any secondary phase, the PMN–PT films had to be sintered in the presence of a PbO-based liquid phase that had to be completely removed from the thick film during the final stage of the sintering. Under optimal sintering conditions we obtained a room temperature relative dielectric permittivity of 3600, dielectric losses of 0.036, a T m of 174 °C, a permittivity at the T m of 21,000 and a d 33 of 140 pC/N.

Marija Kosec

Papers

Transition between the ferroelectric and relaxor states in 0.8 Pb ( Mg 1 ∕ 3 Nb 2 ∕ 3 ) O 3 − 0.2 Pb Ti O 3 ceramics

Homogeneity issues in chemical solution deposition of Pb(Zr,Ti)O3 thin films

Mechanochemical synthesis of NaNbO3

Quasi-one-dimensional domain walls in ferroelectric ceramics: Evidence from domain dynamics and wall roughness measurements

Processing and properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 thick films