Piezoelectric devices with complex electrode geometries often contain ferroelectric regions that experience little or no electric field and remain unpolarised. Since the un-poled and poled material properties differ it is desirable to account for these regions in a device when developing predictive models or to design piezoelectric transducers. The lack of published data on the elastic properties for un-poled ferroelectrics, specifically the numerous commercial compositions such as lead zirconate titanate, reflects the difficulty of experimental measurement. In this work, a method for predicting un-poled properties from more commonly available poled data has been developed. A new method of calculating these properties is presented which provides a rapid and practical solution to the problem of evaluating the isotropic stiffness and Poisson's ratio for an un-poled ferroelectric material. The way in which this calculation has been derived and validated is presented and detailed comparisons are made with alternative methods and experimental data.

Hydroxyapatite (HA), has been used commonly as a bone substitute and as a scaffold in bone tissue engineering. However it has certain drawbacks such as limited biodegradability and osteointegration properties. Other forms of HA, for example, carbonated hydroxyapatite (CHA) could prove to have enhanced bioactivity as they more closely mimic the chemical composition of the apatite found in human bone. The aim of this study was to test the efficacy of CHA in comparison to HA used as a control. The CHA (4.9 wt %) and the HA discs were seeded with MC3T3-E1 osteoblastic cells. Results revealed a trend of increased cell attachment on the HA discs at day 0, however, the cell proliferation on the CHA discs at 7 and 28 days showed no significant difference in comparison to the HA control. SEM of the CHA discs showed surface irregularities at 7 days indicating dissolution. Also at 7 days, SEM demonstrated cell attachment and extracellular matrix production on both the CHA and HA samples. There was no significant difference in the total amount of collagen produced in the CHA samples relative to the HA control samples at 28 days as evaluated by the hydroxyproline assay. Real time PCR revealed mRNA increase by 2.08, 7.62, and 9.86 fold for collagen I a1, collagen III a1, and osteocalcin respectively on the CHA as compared to the HA discs. This study demonstrates the use of CHA as a biocompatible material that has potentially increased biodegradation properties and osteogenic capability in comparison to HA.

This paper aims to review the consistency of existing GaN stiffness data and measure the high temperature elastic moduli of free-standing (0001) GaN. Dynamic mechanical thermal analysis (DMTA) and impact excitation were used to determine the E-33 elastic modulus at room temperature and at temperatures up to 550 degrees C. At room temperature, E-33 ranged from 304 GPa to 279 GPa depending on the specific sample and measurement method. Using DMTA and a calibration with silicon, the elastic modulus decreased by 2.17% between 100 degrees C and 500 degrees C, in close agreement with the literature. By testing samples cut at a range of crystal orientations the isotropy of the stiffness in the (0001) plane was confirmed.

This paper presents a comprehensive impedance spectroscopy comparison of the AC properties of dense stoichiometric TiO2 and conductive TinO2n−1 Magnéli phases over a broad temperature range (up to 1000°C for TiO2 and 375°C for TinO2n−1). The frequency dependent conductivity and permittivity of both materials is explained in terms of “universal” power law behaviour. A deviation from the law, with a giant relative permittivity which is largely independent of frequency from 0.1Hz to 100–200kHz is observed in the case of TinO2n−1, due to the presence of residual TiO2 generating an Internal Barrier Layer Capacitor (IBLC) effect. The real–imaginary impedance plots are interpreted using an RC model and allow separation of the contribution of the grain bulk and the grain boundaries to the total resistivity of the material. In the case of the TinO2n−1 based materials this confirms that the IBLC effect is generated by insulating grain boundaries. The conduction mechanism in both TiO2 and TinO2n−1 appears to be dominated by electronic conductivities, activated mainly through shallow donor levels up to 200°C and over the entire band gap, which is narrower for TinO2n−1, above 200°C. A deeper understanding of the AC properties of Magnéli phases of Ti at different temperatures aids in the optimisation of electrical properties for a variety of sensor and electrical applications.

This letter presents a comprehensive impedance spectroscopy characterisation of Magnéli phases (TinO2n-1) over a range of temperatures, which are of interest in electrochemistry and sensing applications, with the aim to enhance the understanding of their electrical properties and influence their microstructure. The impedance of the TinO2n-1 can be resolved into two different contributions, namely the grain bulk (RB) and grain boundaries (RGB). The ac conductivity increases with frequency and temperature, following a universal power-law. The high relative permittivity (10-10), which is relatively frequency independent from 0.1Hz to 100kHz, is attributed to the presence of insulating grain boundaries (RGB>>RB) creating an Internal Barrier Layer Capacitor (IBLC) effect. Above 100kHz, the grain boundaries begin to contribute to the ac conductivity and the permittivity drops sharply.

This letter presents a comprehensive impedance spectroscopy characterisation of Magnéli phases (TinO2n−1) over a range of temperatures, which are of interest in electrochemistry and sensing applications, with the aim to enhance the understanding of their electrical properties and influence their microstructure. The impedance of the TinO2n−1 can be resolved into two different contributions, namely the grain bulk (RB) and grain boundaries (RGB). The ac conductivity increases with frequency and temperature, following a universal power law. The high relative permittivity (105–106), which is relatively frequency independent from 0.1Hz to 100kHz, is attributed to the presence of insulating grain boundaries (RGB>>RB) creating an Internal Barrier Layer Capacitor (IBLC) effect. Above 100kHz, the grain boundaries begin to contribute to the ac conductivity and the permittivity drops sharply.

Micromechanical models of porous ferroelectric ceramics have often assumed that the material is fully polarized in a particular direction and/or consists of a single isolated pore. In this work the polarization state in three-dimensional porous polycrystalline ferroelectric networks has been modelled to eradicate the oversimplification of these idealized unit cells. This work reveals that microstructural network models more closely represent a porous ferroelectric microstructure since they are able to take into account the complex polarization distribution in the material due to the presence of high and low permittivity regions. The modelling approach enables the prediction of the distribution of poled and unpoled material within the structure. The hydrostatic figures of merit and permittivity were determined for a variety of porous lead zirconate titanate microstructures and found to be in good agreement with experimental data. The decrease in piezoelectric activity with porosity was observed to be associated with the complex polarization state within the material. Model results were shown to be much improved when compared to a model assuming a fully polarized model.

Simple and contactless methods for determining the health of metallic and composite structures are necessary to allow non-invasive Non-Destructive Evaluation (NDE) of damaged structures. Many recognized damage detection techniques, such as frequency shift, generalized fractal dimension and wavelet transform, have been described with the aim to identify, locate damage and determine the severity of damage. These techniques are often tailored for factors such as (i) type of material, (ii) damage patterns (crack, impact damage, delamination), and (iii) nature of input signals (space and time). In this paper, a wavelet-based damage detection framework that locates damage on cantilevered composite beams via NDE using computer vision technologies is presented. Two types of damage have been investigated in this research: (i) defects induced by removing material to reduce stiffness in a metallic beam and (ii) manufactured delaminations in a composite laminate. The novelty in the proposed approach is the use of bespoke computer vision algorithms for the contactless acquisition of modal shapes, a task that is commonly regarded as a barrier to practical damage detection. Using the proposed method, it is demonstrated that modal shapes of cantilever beams can be readily reconstructed by extracting markers using Hough Transform from images captured using conventional slow motion cameras. This avoids the need to use expensive equipment such as laser doppler vibrometers. The extracted modal shapes are then used as input for a wavelet transform damage detection, exploiting both discrete and continuous variants. The experimental results are verified using finite element models (FEM).

This version is made available in accordance with publisher policies. Please cite only the published version using the reference above. Abstract This letter presents a comprehensive impedance spectroscopy characterisation of Magnéli phases (Ti n O 2n-1) over a range of temperatures, which are of interest in electrochemistry and sensing applications, with the aim to enhance the understanding of their electrical properties and influence their microstructure. The impedance of the Ti n O 2n-1 can be resolved into two different contributions, namely the grain bulk (R B) and grain boundaries (R GB). The ac conductivity increases with frequency and temperature, following a universal power-law. The high relative permittivity (10 5-10 6), which is relatively frequency independent from 0.1Hz to 100kHz, is attributed to the presence of insulating grain boundaries (R GB >>R B) creating an Internal Barrier Layer Capacitor (IBLC) effect. Above 100kHz, the grain boundaries begin to contribute to the ac conductivity and the permittivity drops sharply.

This article describes the processing and characterisation of lanthanum-doped lead zirconate titanate (PLZT)-based ferroelectric fibres for composite transducer applications. X-ray diffraction of the extruded and sintered fibres indicated some lead loss during sintering; however, the fibres exhibited low porosity (1.54%), high maximum piezoelectric strain (4041 ppm) and relatively low coercive field (0.77 kV/mm). The low coercive field of the lanthanum-doped fibres may be advantageous in terms of facilitating polarization of the fibres in composite architectures.

This study focuses on porous ceramics as a promising new type of anode material for photo-microbial fuel cells (p-MFCs). The anodes were made from titanium dioxide and chemical vapour deposition was used to coat them with a layer of fluorine doped tin oxide (FTO) to make them conducting. Chlorella vulgaris biofilms were grown in the millimetre sized pores of the ceramic electrodes, producing an extensive extra cellular matrix that was anchored directly to the electrode surface. In contrast algal cells grown on carbon felt appeared misshapen and lacked a continuous extra cellular matrix. A preliminary comparison of different anodes in p-MFCs showed that the power density was similar to 16 times higher on a ceramic anode compared to the best performing carbon anode. Good power densities were also found for algae grown directly onto FTO coated glass, but in contrast to the ceramic anodes the biofilm did not adhere strongly to the planar surface and was easily removed or damaged.

Advanced piezoelectric devices increasingly demand materials that can provide both an improved electrical and mechanical response. For many applications, it is vital that the material engineer can characterize how stresses will influence the material and device response. In this paper measurement methods have been developed to simultaneously characterize the mechanical and piezoelectric performance of small lead zirconate titanate (PZT) tubes subjected at high stress. The influence of PZT composition and poling direction has been considered. The effects of stress on the non-linear mechanical response are discussed with respect to observations made by impedance analysis. These findings will guide material selection for enhanced sensor and actuator design.

Electrical potentials in mechanically loaded bone have been implicated as signals in the bone remodeling cycle. Recently, interest has grown in exploiting this phenomenon to develop electrically active ceramics for implantation in hard tissue which may induce improved biological responses. Both polarized hydroxyapatite (HA), whose surface charge is not dependent on loading, and piezoelectric ceramics, which produce electrical potentials under stress, have been studied in order to determine the possible benefits of using electrically active bioceramics as implant materials. The polarization of HA has a positive influence on interfacial responses to the ceramic. In vivo studies of polarized HA have shown polarized samples to induce improvements in bone ingrowth. The majority of piezoelectric ceramics proposed for implant use contain barium titanate (BaTiO3). In vivo and in vitro investigations have indicated that such ceramics are biocompatible and, under appropriate mechanical loading, induce improved bone formation around implants. The mechanism by which electrical activity influences biological responses is yet to be clearly defined, but is likely to result from preferential adsorption of proteins and ions onto the polarized surface. Further investigation is warranted into the use of electrically active ceramics as the indications are that they have benefits over existing implant materials.

Composite silicon–polycrystalline chemical vapour deposition (CVD) diamond wafers are potential substrates for GaN-based devices for use in harsh environments due to their high thermal conductivity and chemical stability. When cooled from a typical diamond deposition temperature of approximately 800 to 25 °C wafer bowing arises from a mismatch in the coefficients of thermal expansion of silicon and polycrystalline diamond. In this paper 100 mm diameter silicon–polycrystalline diamond wafers have been modelled using ANSYS finite element software to investigate their bowing behaviour as a function of temperature and geometry. The maximum bow of a wafer occurred where the thicknesses of both the silicon and polycrystalline diamond layers was almost identical; this has been confirmed using analytical methods. Strategies are discussed for reducing wafer bow.

The harmonic response and modal shapes of axially-symmetrical piezoceramic cylinders (tubes) polarised through the wall thickness have been predicted by finite element methods and determined experimentally. Analysis of ceramic cylinders has concentrated on the effects of the variation of diameter to thickness (d/t) ratios, and change in cylinder length (l). Investigation has taken into account material variance and vibration performance with relation to both ‘hard’ and ‘soft’ type ceramics. Computational finite element modelling (ANSYS) and numerical techniques has allowed for the prediction of the harmonic response and modal shapes, thus enabling the choice of cylinder geometry and performance. Resonant frequencies of piezoceramic cylinders have been determined experimentally by impedance analysis. The changes in resonant frequencies have been determined for a range of d/t and l/d ratios and for a variety cylinder of lengths. Predictions of harmonic response of the piezoceramic cylinders are shown to agree well with experimental results, with identification of the modal shapes.

This paper discusses the formation of complex geometry electrode structures on piezoelectric ceramic substrates using nanosecond pulsed laser ablation. Optical microscopy, scanning electron microscopy and surface profiling are used to examine the impact of the laser ablation process onto the substrate material. The influence of laser power, pulse energy and scanning speed on electrode removal and potential substrate damage is discussed. Fabricated prototypes with different electrode designs and potential sensing applications are presented.

Results on manufacturing and electromechanical properties of hydroxyapatite / BaTiO3 ceramic composites with ceramic volume fractions m 0.7 are reported. Experimental volume-fraction dependences of the piezoelectric coefficients d 31*(m), d 33 * (m) and dielectric permittivity 33 * (m) are explained using a composite model in terms of 1-3 and 2-2 connectivity.

This paper studies the effect of porosity on the electrical properties and polarisation behaviour of hydroxyapatite based ceramics prepared in both dense and porous form. Porosity was introduced into the hydroxyapatite using either burnt-out polymer spheres to produce isolated pores or using polymer foams to create interconnected porosity. The samples were sintered in water vapour at 1300°C and polarised at 400°C with a dc voltage of 3kV/cm applied for 1 hour. Thermally stimulated depolarisation current measurements were used to investigate the degree of polarisation of the hydroxyapatite ceramics and dielectric spectroscopy used to measure the ac conductivity of the materials at the polarisation temperature. The porous materials were successfully polarised and the presence of a high surface area to volume ratio in the porous samples was thought to increase the level of polarisation.

This paper studies the ac conductivity and permittivity of hydroxyapatite based ceramics (HA) at temperatures from room temperature to 1000oC. HA ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of surface adsorbed water on conductivity and permittivity. Surface bound water was thought to contribute to conductivity for both dense and porous materials at temperature below 200oC. At temperatures below 700oC the permittivity and ac conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000oC), bulk ionic conduction was dominant and activation energies are in the range of ~2eV, indicating that hydroxyl ions are responsible for conductivity.

Porous lead magnesium niobate-lead titanate (PMN-PT 90:10) relaxors were impregnated with water to provide a model conductor-insulator mixture, to study their power law frequency dependency of ac conductivity, permittivity and phase angle. Relaxor materials with a range of open porosity filled with water created composites with conductor volume fractions ranging from 8.2% to 22.2%. The use of a high relative permittivity PMN-PT (∼ 8000) enabled the power law dispersion to be observed at relatively low frequencies (∼ 2 kHz). Good agreement was obtained between experimental data and predicted results based on a logarithmic mixing rule with a strong correlation between the power law exponent and conductor-insulator fraction. The model and numerical methods presented are considered a simple approach to interpret and predict and the frequency dependent properties of materials which similar heterogeneity.