Conducting domain walls (DWs) in ferroelectrics is an emerging research focus in nano-electronics... more Conducting domain walls (DWs) in ferroelectrics is an emerging research focus in nano-electronics . Previously overlooked, these walls have recently been reported to possess diverse functional characteristics that are completely different from the domains that they delineate . They can have their own distinct chemistry and magnetic behavior , and in turn represent a completely new sheet phase. The characteristics of these confined regions are believed to have the same exotic functional behaviours as seen in 2D materials such as graphene, opening up a plethora of possible electronic applications. In addition, the walls have the unique property of being 'agile'; they can be created or destroyed and even be controllably moved by an external field. However, this is an area of research at its very early stages, with a great deal of the fundamental physics still unknown. Since the region of interest (the domain wall) is atomically thin and dynamic, it is essential for the physical characterization to be at this scale and be time-resolved.
Ferroelectric domain walls constitute a completely new class of sheet-like functional material. M... more Ferroelectric domain walls constitute a completely new class of sheet-like functional material. Moreover, since domain walls are generally writable, erasable and mobile, they could be useful in functionally agile devices: for example, creating and moving conducting walls could make or break electrical connections in new forms of reconfigurable nanocircuitry. However, significant challenges exist: site-specific injection and annihilation of planar walls, which show robust conductivity, has not been easy to achieve. Here, we report the observation, mechanical writing and controlled movement of charged conducting domain walls in the improper-ferroelectric Cu3B7O13Cl. Walls are straight, tens of microns long and exist as a consequence of elastic compatibility conditions between specific domain pairs. We show that site-specific injection of conducting walls of up to hundreds of microns in length can be achieved through locally applied point-stress and, once created, that they can be move...
Caracterización por medio de microscopía electrónica de transmisión de cerámicas de titanato zirconato de plomo con alto contenido en Zr
This work presents a Transmission Electron Microscopy (TEM) study of a series of ceramics with co... more This work presents a Transmission Electron Microscopy (TEM) study of a series of ceramics with compositions Pb(Zr 1-x Ti x )O 3 (0.06≤x≤0.45). Two ferroelectric rhombohedral phases have been identified within this range of compositions. Besides the characterization of the domain configuration, TEM allows to obtain information of the local crystalline structure of these phases. One of the characteristics observed in these phases is the appearance of superlattice reflections at 1/2 {110} p and 1/2 {111} p positions of the electron diffraction patterns, which have not been observed by neutron or X-ray diffraction. They disappear when the paraelectric cubic phase is reached and with the increase of the Ti content. Dark field micrographs obtained with these reflections reveal details of the structures associated with them. The origin of these superlattice reflections has been attributed by other authors to a system of oxygen octahedra tiltings, which cannot explain the presence of some specific reflections. From the results we conclude that a more plausible explanation is the appearance of antiparallel displacements of cations.
Uncooled infrared thermal detector arrays. [Proceedings of SPIE 1320, 88 (1990)]. NM Shorrocks, S... more Uncooled infrared thermal detector arrays. [Proceedings of SPIE 1320, 88 (1990)]. NM Shorrocks, Stephen G. Porter, Roger W. Whatmore, Andy D. Parsons, JN Gooding, David J. Pedder. Abstract. Uncooled detectors of infra-red ...
Piezoelectric and Pyroelectric Materials and Their Applications
Electronic Materials, 1991
The phenomenon of piezoelectricity, the release of electric charge under the application of mecha... more The phenomenon of piezoelectricity, the release of electric charge under the application of mechanical stress, occurs in all noncentrosymmetric materials. Pyroelectricity, the release of charge due to a material’s change of temperature, occurs in all materials that belong to a polar crystal symmetry class. It should be noted that, as not all noncentrosymmetric classes are polar (222, 4, 422, \(\overline 4 2m\), 32, 6, 622, \(\bar 6m2\), 23, and \(\bar 43m\) are the nonpolar, noncentrosymmetric classes), not all piezoelectric crystals are pyroelectric. However, all pyroelectric crystals are piezoelectric. (As a final note, crystals belonging to the noncentrosymmetric cubic class 432 are nonpiezoelectric because all the piezoelectric moduli vanish under the operation of the symmetry elements.) Ferroelectrics form a subset of the set of pyroelectrics because they are polar materials in which the direction of the polar axis can be changed by the application of an electric field. As a consequence they are both pyroelectric and piezoelectric. As many of the largest pyroelectric and piezoelectric effects occur in ferroelectric materials, they have become very important technologically. Furthermore, the fact that the polar axis can be reoriented by the application of a field means that polycrystalline ferroelectrics in which the crystallographic axes of the component crystallites are randomly oriented can be made to show polar properties by applying a sufficiently large electric field (the process of “poling”).
Thin ferroelectric films for thermal detector applications
Integrated Ferroelectrics, 1992
The deposition of thin films of lead scandium tantalate (Pb(Sc1/2Ta1/2O3) have been investigated ... more The deposition of thin films of lead scandium tantalate (Pb(Sc1/2Ta1/2O3) have been investigated by two processing routes. In the first, progress is reviewed for chemical vapour deposition in a purpose built low pressure reactor, utilising suitable modified proprietary precursors. Deposition has been studied over the temperature range 400–800°C and, in general, amorphous films result which convert to crystalline perovskites on
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2006
Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (... more Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (Ti) (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free, single-layer films of 70-nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free, single layers up to 200 to 300 nm thick, which can be built-up into layers up to 3-m thick. Thicker PZT films (> 2-m single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electroactive properties of these materials is essential for modeling and design of novel micro-electromechanical systems (MEMS) devices, but accurate measurement of these properties is by no means straightforward. A novel, double-beam, commonpath laser interferometer has been developed to measure the longitudinal (d33) piezoelectric coefficient in films; the results were compared with the values obtained by Berlincourt and laser scanning vibrometer methods. It was found that, for thin-film samples, the d 33 f values obtained from the Berlincourt method are usually larger than those obtained from the interferometer and the vibrometer methods; the reasons for this are discussed.
Finite element modelling of nanostructured piezoelectric resonators (NAPIERs)
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2004
A new modification to the traditional piezoelectric thin film bulk acoustic wave resonator (FBAR)... more A new modification to the traditional piezoelectric thin film bulk acoustic wave resonator (FBAR) and solidly mounted acoustic wave resonator (SMR) is proven to significantly improve their performances. The proposed design involves the surface micro/nano structuring of planar piezoelectric thin films to realize an array of a large number of rod-like structures. In contrast to the plate-like thickness extensional resonance in traditional FBAR and SMR devices, the rod-like structures can be excited in their length extensional resonance, yielding a higher electromechanical coupling factor and effectively eliminating the spurious resonances from lateral modes of vibration. The designs have been investigated by two and three-dimensional finite element analyses and one-dimensional transmissionline modelling. The results show that significant increases in the electromechanical coupling factor of ca. 40% can be achieved by using the rod-like length extensional resonances as compared with the plate-like thickness extensional resonances in traditional devices. Simulations show that rod width-to-thickness aspect ratios of less than 0.5 could result in an electromechanical coupling factor (k2eff) of over 10% for a zinc oxide device, compared with approximately 7% for a conventional design.
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Papers by Roger Whatmore