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FLASH sintering is a field-assisted technique that allows the densification of ceramics in a few seconds at temperatures significantly lower than those of conventional cycles. There is still discussion among the scientific community about the mechanism behind this sintering process, that has been typically attributed to Joule heating, defect creation and movement or liquid phase assisted sintering. Computational modelling can be a powerful tool in helping to explain and predict this process. Using potassium sodium niobate (KNN) as a case study, a lead-free piezoelectric, this work explores Finite Element Modelling to evaluate the dependence of Joule heating generation and temperature distribution as a function of the cubic particle orientation. [ABSTRACT FROM AUTHOR]

Cubic bismuth zinc niobate (c-BZN) thick films were fabricated on flexible platinum foils by electrophoretic deposition technique. The X-ray diffraction studies reveal that the films are under tensile stress. The permittivity of the c-BZN thick film sintered at 850 and 950°C, measured at an applied frequency of 1 MHz were 114 and 125, respectively. The corresponding values of dissipation factors were 0.004 and 0.0038. The films were also exhibiting voltage-dependent dielectric properties. The biaxial tensile stress, which is developed as a result of substrate constraints during the sintering, leads to significant change in the relaxation and dielectric characteristics of the films compared to that of ceramics. From this study, it is expected that large tensile stress in c-BZN thick films can bring down the dielectric loss and the variation of the dielectric permittivity with temperature, which will make them attractive, low loss and temperature stable applications. [ABSTRACT FROM AUTHOR]

The temperature dependence of the dielectric properties and ac conduction of YMnO3 ceramics annealed under different atmospheres is investigated from 25 to 700 °C. The origin of the dielectric anomalies is clarified. Two dielectric peaks in the permittivity accompanied by a single anomaly in the dielectric losses characterize the dielectric response. Simultaneously, three different regions can be distinguished in the temperature dependence of ac conductivity. Oxygen vacancies with an activation energy for the conduction of 1.13 eV are suggested to be responsible for the dielectric anomaly observed at < 400 °C. For temperatures > 400 °C, the dielectric data are influenced by conductivity and no ferroelectric anomaly is obvious. [ABSTRACT FROM AUTHOR]

The dc electric-field dependence of the dielectric constant [variant_greek_epsilon]′(E) in Sr1-xMnxTiO3 (x=0.005-0.02) ceramics is studied in the temperature range from 10 to 125 K, i.e., around the [variant_greek_epsilon]′(T) peak temperature Tmax. Results are analyzed using equations derived analytically from the implicit equations of the Landau-Ginzburg-Devonshire (LGD) theory. Corrections due to cluster contribution attributed to the reorientation of random-field-induced polar nanometer-scale regions turn out to be important, if not decisive, for a reliable description of [variant_greek_epsilon]′(E). So, it is found that a combined equation including the Langevin-type cluster term, i.e., [variant_greek_epsilon]L′(E)=P02L3/(2kBT[variant_greek_epsilon]0[cosh(P0L3E/2kBT)]2) is the most suited to describe the dc electric-field dependence of the dielectric constant around Tmax. Based on the fitting of the [variant_greek_epsilon]′(E) data, the cluster polarization P0 reaches values as high as ∼0.4 μC/cm2 with the cluster size L of 11±4.5 nm. Thus, the existence in the Sr1-xMnxTiO3 system of polar clusters with nanometer-scale size is consistent with [variant_greek_epsilon]′(E) data and their contribution to the permittivity at E=0 and temperatures close to Tm is estimated to be up to 30%. In addition, besides inducing the peak in [variant_greek_epsilon](T), the formation of polar nanoregions is beneficial to the high relative electric-field tunability of the dielectric constant nr=[[variant_greek_epsilon]′(0)-[variant_greek_epsilon]′(E)]/[variant_greek_epsilon]′(0)∼70% as well as high communication quality factor K=[[variant_greek_epsilon]′(0)/[variant_greek_epsilon]′(E)-1]2/[[variant_greek_epsilon]′(0)/[variant_greek_epsilon]′(E)tan δ(0)tan δ(E)]∼10 000 under 20 kV/cm at 10 kHz. [ABSTRACT FROM AUTHOR]

An alternative low cost flexible processing is utilized to fabricate tunable dielectric thick-films with low loss. By using a combination of electrophoretic deposition with chemical solution deposition, 9 μm-thick BaNd 2 Ti 5 O 14 -Ba 0.5 Sr 0.5 TiO 3 (BNT-BST) composite films are fabricated with a room-temperature relative permittivity of 287 and a loss tangent of 0.0013 at 1 MHz. Moreover, a dielectric tunability and a figure of merit of 12% and 96 at 33 kV/cm, respectively, are obtained by the incorporation of highly tunable ferroelectric BST in a non tunable BNT matrix, thus fitting the requirements of tunable dielectrics for such agile systems as band pass filters. [ABSTRACT FROM AUTHOR]

Titanium-rich (Sr/Ti = 0.995) strontium titanate (ST) ceramics, air-sintered in a temperature range of 1400–1625 °C, were reported to possess anomalies in the grain growth and analogous anomalies in the grain boundary (GB) conductivity activation energy. However, these two interface-related phenomena, occurring at GBs, could not be associated with each other using a simple “brick-layer” model. In this work we revise the topic and advocate that the deviation from the model comes from the oxygen vacancies localized at GBs of the rapidly-cooled ST ceramics. To verify this, we annealed the ceramics in oxygen and performed their systematic and comparative analysis using impedance spectroscopy. A levelling-off in the GB conductivity activation energy, which increases for ≤1.24 eV, and a four-fold decrease in the GB permittivity are observed after annealing. Thus, we confirm a key role of oxygen vacancies in relation between the grain growth and GB conductivity anomalies of as-sintered Ti-rich ST ceramics. [ABSTRACT FROM AUTHOR]

Microvalves used to control gas flow in water heaters are traditionally based on low cost ubiquitous solenoid technology. The demand for a better flux control and for reducing the dependence on the solenoid Cu and rare earth magnetic materials, underlines the need for alternative solutions. In this work we report an engineering case study with experimental validation where a substituting solution to a commercial heater solenoid microvalve is provided by a low-cost high stroke piezoelectric bender for gas flow control. We established the relations between applied voltages, bender displacements, gas pressure drops through the microvalve and associated flow rates and demonstrate that the operation conditions of the piezoelectric microvalve resemble those of the solenoid one. By manipulating the electrical potential difference applied to the bender it is possible to control the pressure drop associated with the microvalve. The piezoelectric microvalve behaves in a continuous mode, not as a on-off device, what is a significant advantage over the solenoid one. We have proven that it is possible to directly incorporate a piezoelectric bender in a commercial solenoid- driven microvalve without significant changes in the valve design. The resultant piezoelectric driven valve is faster, partial, high voltage but low current, and silent. [Display omitted] • alternative solutions to solenoid technology for microvalves for control gas flow in water heaters. • experimental validation of a substituting low-cost high stroke piezoelectric bender for gas flow control. • operation conditions of piezoelectric microvalve resemble those of the solenoid. • manipulating electrical potential difference applied to the bender, pressure drop associated with the microvalve controlled. • continuous mode operation for piezoelectric microvalve versus a on-off solenoid one. [ABSTRACT FROM AUTHOR]

Temperature stable dielectrics of tungsten bronze Sr 4 Nd 2 Ti 4 Nb 6 O 30 (SNTN) with maximized dielectric performance are achieved with thick films prepared by electrophoretic deposition. 30 μm thick SNTN films sintered at 1300 °C, exhibit permittivity ɛ > 375, loss tangent tanδ < 0.01 and stable to ±7.5% of the room temperature value in the temperature range of −95 °C to 280 °C. This permittivity is ∼34% higher than that for bulk ceramics (∼280) processed under the same conditions. Contrary to the microstructure of ceramics, SNTN thick films exhibit anisotropy of the grain growth with increasing sintering temperature. It is proposed that the observed anisotropy is responsible for the maximization of the dielectric properties and is due to the anisotropic crystal structure of SNTN and to the sintering under constraint. The main contribution of the c axis vibration to the dielectric constant in tungsten bronze SNTN is confirmed. These results are relevant because via tailoring the substrate constraint and sintering conditions the grain anisotropy of SNTN thick films can be controlled and thus the dielectric properties. [ABSTRACT FROM AUTHOR]

Thick films of functional oxides are currently substituting counterparts bulk ceramics, as in the case of low loss dielectrics. For SrTiO 3 (ST) based compositions it is demonstrated that electrophoretic deposition (EPD), using acetone as a suspension media with iodine addition, is a suitable technology to fabricate 12 μm thick films. The microstructural analysis of the films sintered at 1500 °C shows that highly densified microstructures can be obtained and, by slightly varying the Sr/Ti stoichiometry in the powder composition, increased densification and grain size and enlargement of the distribution with decreasing Sr/Ti ratio can be observed. In spite of the high densification of the films, it is also demonstrated that due to the constraint imposed by the substrate a smaller grain size is observed in thick films as compared to equivalent bulk ceramics. In addition, a preferential vertical pore orientation is observed in ST thick films. These results may have broad implications if one considers that the dielectric losses and dielectric tunability is affected by pore orientation, since it affects the electric field distribution. [ABSTRACT FROM AUTHOR]

The voltage dependence of the dielectric permittivity ε′ and the low dielectric loss tanδ of incipient ferroelectrics have drawn vast attention to the use of these materials for the development of tuning elements in electronics and telecommunications. Here, we study the DC electric field dependence of low-temperature ε′ in ~320 nm thick sol-gel-derived SrTi1−xZnxO3−δ thin films with x = 0.01 and 0.05, deposited on Pt/TiO2/SiO2/Si substrates. Incorporation of Zn onto Ti sites is found to decrease ε′ compared to undoped SrTiO3 films, while increasing the relative tunability nr up to ~32.9% under a DC electric field of 125 kV/cm at low temperatures. The hysteresis-free variation in ε′ with electric field and tanδ values below 0.6% observed for SrTi1−xZnxO3−δ film with x = 0.01 make this compound more attractive for tunable device applications. [ABSTRACT FROM AUTHOR]

Abstract: The use of functional materials, such as ferroelectrics, as platforms for tissue growth in situ or ex situ, is new and holds great promise. But the usage of materials in any bioapplication requires information on biocompatibility and desirably on bioactive behavior when bone tissue engineering is envisaged. Both requirements are currently unknown for many ferroelectrics. Herein the bioactivity of LiNbO3 and LiTaO3 is reported. The formation of apatite-like structures on the surface of LiNbO3 and LiTaO3 powders after immersion in simulated body fluid (SBF) for different soaking periods indicates their bioactive potential. The mechanism of apatite formation is suggested. In addition, the significant release of lithium ions from the ferroelectric powders in the very first minutes of soaking in SBF is examined and ways to overcome this likely hurdle addressed. [Copyright &y& Elsevier]

Abstract: Due to the increasing availability of substitute materials for electrical porcelain, research is needed to adapt formulations involving these materials to the current economic realities of the industry. This study assessed the effect of iron oxide concentration (0, 1, 2, 3, 5, and 8wt%) on the dielectric properties of an aluminous porcelain composition commonly employed for electrical insulation based on different values of temperature and frequency. Samples with iron oxide contents of 0, 3, and 5wt% were analyzed using dilatometry, X-ray diffraction, and scanning electron microscopy to evaluate the thermal, structural, and microstructural changes related to their Fe2O3 concentrations. Both the dielectric constant (ε r) and the loss tangent (tan δ) were measured and evaluated in every sample. Results indicated that the presence of Fe2O3 increased the dielectric constant and loss tangent, which could result in an increase in heating by dielectric losses. Fe2O3 contents of up to 5wt% had no significant effect on the performance of these insulators at room temperature (∼30°C) and a high frequency (1MHz), especially when the hematite phase was completely solubilized in the porcelain phases. [Copyright &y& Elsevier]

The importance of electrophoretic deposition (EPD) iswell recognizedfor thick film technology, but unfortunately there is no universalsuspension medium for the EPD of oxides. Thus, the selection of themedium, the stability of the suspensions, and the control of the particlepotentials, critical for a good deposition, need to be establishedfor each new material being processed by EPD. In this article, weinvestigate the key parameters, studying the electrochemistry of BaNd2Ti5O14(BNT) suspensions, and establishrelationships between suspension media, EPD process conditions, microstructureof the deposits, and resulting electrical properties of the BNT films.Suspension stability of water, ethanol, acetic acid, and acetone-basedmedia was analyzed in terms of zeta potential, particle size distribution,UV transmittance, and inductively coupled plasma spectrometry. Thehighest absolute zeta potential values determined for acetone withI2and acetic acid media are in good agreement with thehigh stability, small and narrow particle size distribution, and lowUV light transmittance measured for these suspensions. Very high qualitythick deposits were consequently achieved. However, it was demonstratedthat aging of the acetic acid-based suspension have serious negativeeffects on the EPD process for BNT materials, including leaching ofthe metallic elements with a consequent modification of the materialstoichiometry, change of the conductivity of the suspension, and degradationof the films microstructure. These facts severely restrict the useof acetic acid. Our results clearly indicate that, besides the stabilityof the suspension, the electrochemistry and aging behavior are keyaspects for the EPD of functional oxides. Our systematic approachcould be viewed as providing a set of guidelines for the developmentof EPD of other oxides. [ABSTRACT FROM AUTHOR]

Abstract: Electrophoretic deposition has been successfully used for the preparation of multilayer composite thick films of the temperature stable microwave dielectric ceramics BaLa4Ti4O15 (BLT) (ɛ r =44, Qf 0 =44,000GHz) and Ba4Nd9.33Ti18O54 (BNT) (ɛ r =82, Qf 0 =10,000GHz). The composites exhibit permittivity intermediate between the end members that may be tuned by modifying the ratio between and/or thickness of each layer, thereby tailoring the films for specific applications. In demonstrating an alternative way to tailor functional properties, these results have broad implications for a large number of thick film-based devices. [Copyright &y& Elsevier]

Abstract: Potassium tantalate (KTaO3 – KT) ceramics with controlled initial K/Ta ratio=1, 1.02 and 1.05 were synthesised by solid-state reaction. Crystal structure and microstructure of the sintered ceramics were examined by XRD and SEM/EDS, respectively. Their dielectric properties were then studied as a function of the temperature over the radio frequency range. Ceramics with K/Ta ratio=1 exhibits potassium-poor secondary phases, in contrast to ceramics with initial K/Ta ratio=1.05, where no secondary phases are detected. Moreover, the grain size increases dramatically with K/Ta ratio >1. The quantum paraelectric behaviour of KT ceramics is weakly affected by the variation of K/Ta ratio and their dielectric response is well described by Barrett''s equation. Though, no anomaly is induced in the dielectric permittivity by potassium excess, it yields an increase of its lowest temperature magnitude up to ∼4000, which is to the best of our knowledge, the highest value ever reported for KT ceramics. [Copyright &y& Elsevier]

Abstract: Lead zirconate titanate (PZT, 53/47) fibers are prepared by sol–gel method using organic acids – acrylic and methacrylic acid – to modify the precursors. The macroscopic properties, molecular structure, crystallization behaviour and microstructure of the fibers are investigated as a function of the content and type of acid. Organic acids produce long gel and ceramic fibers, due to the beneficial effect of the long polymeric chains that are generated in the precursor gel. However the longest, strongest, densest and with the highest homogeneity fibers are obtained when acrylic acid is used. The linear shape of the molecular structure of acrylic acid, together with a lower content of organic species to be released, is favourable to the preparation of round and crack free PZT fibers, when acrylic acid is used. [Copyright &y& Elsevier]

High-quality potassium tantalate (KTaO3, KT) single crystals are grown by a high-temperature self-flux solution modified method in which potassium carbonate (K2CO3) and boron oxide (B2O3) are utilized as a complex flux. Additions of small amounts of boron oxide, used because of its low melting temperature (450 °C) and tendency to decrease the weight losses, increased the metastable region, requiring lower temperature (≤1300 °C) for the growth of relatively large KT crystals thereby suppressing the K volatilization tendency. By changing the flux composition and flux to solute proportion growth conditions are modified. The as-grown potassium tantalate crystals exhibit a dielectric permittivity of 6600 and dielectric losses of 0.004 at 13 K and 100 kHz. These results suggest a new promising approach for growing relatively large size and high quality single crystals within KT-based system. High-quality KTaO3 single crystals grown by a high temperature self-flux solution modified method, in which potassium carbonate (K2CO3) and boron oxide (B2O3) are utilized as a complex flux, exhibit a dielectric permittivity of 6600 and dielectric losses of 0.004 at 13 K and 100 kHz. [ABSTRACT FROM AUTHOR]

Crystalline (Ba xSr1− xTiO3) ( x = 0, 0.5 0.8 and 1) nanosized powders is synthesized by an ambient pressure and low temperature sol process. The influence of Ba/Sr ratio, temperature, pH and reflux time on the phase formation and morphology of (Ba xSr1− xTiO3) powders is assessed. Amorphous powders are obtained at temperatures lower than 90 °C and crystalline, stoichiometric and monophasic Ba xSr1− xTiO3 ( x = 0, 0.5, 0.8 and 1), powders are synthesized at 95 °C. Under identical preparation conditions, the powder particle size depends on the Ba/Sr ratio. High values of pH decrease the particle size. For reflux times lower than 2 h the particle size decreases with increasing of reflux time, reflecting the dominant role of the nucleation step. For reflux times higher than 2 h the growth step becomes dominant and the particle size increases with the increase of reflux time. [ABSTRACT FROM AUTHOR]

Abstract: Functional oxides on Cu have multiple applications. For thick films the required high sintering temperatures present a challenge for processing on base metal substrates. In this study it is shown that it is possible to adapt well-known ceramic processing strategies to the fabrication of thick lead zirconate titanate (PZT) films on Cu with useful ferroelectric properties. PZT powders with optimized particle sizes are used to fabricate thick films by electrophoretic deposition in combination with a post-deposition isostatic pressing step. This approach to maximize green packing is sufficient to dramatically lower the required sintering temperatures. 25μm thick PZT films on Cu sintered at 900°C have a dielectric permittivity of 585, a loss tangent at 10kHz of 0.03, a remanent polarization of 19μCcm−2 and a coercive field of 22kVcm−1. This significant improvement in the dielectric response opens the possibility of using thick PZT films on Cu for a wide range of devices where cost, yield and reliability are concerns. [Copyright &y& Elsevier]

Abstract: SrTiO3:Mn ceramics, prepared according to the chemical formulae Sr1– x Mn x TiO3 and SrTi1– y Mn y O3, are studied by Fourier transform infrared and time-domain terahertz spectroscopy in the temperature range of 10–300K to support the incorporation of Mn ions into the perovskite lattice of SrTiO3, and to ascertain their different lattice site locations. The polar soft mode of the incipient ferroelectric SrTiO3 is found to be hardened in the whole temperature range by the substitution of Mn ions on Ti sites, and only in the low-temperature range by the Sr site substitution. Activation of the mode, associated with the R point condensation of the Brillouin zone due to the doubling of the unit cell by antiphase rotations of the O-octahedra below the structural transition temperature T a, shows that the substitution of Mn ions on the Sr sites increases T a, whereas the Ti-site substitution suppresses T a with respect to the undoped SrTiO3. [Copyright &y& Elsevier]

In this paper we report on a development of a new method for measurements of electric field-induced displacements in a cylindrical geometry (optical fiber with the deposited piezoelectric film). The measurement setup is based on a commercially available Fotonic Sensor MTI 2000 (MTI Inc.). Major disadvantages of measurement by standard techniques (e.g., interferometry) such as low reflectivity, high roughness of the coating resulting in poor fringe quality, and big displacement range are successfully avoided using a special configuration of an optical probe and a sample. The method allows performing investigations of electromechanically induced vibrations in a broad frequency range (from 0 up to 150 kHz) and various combinations of ac and dc voltages. The capabilities of the proposed method are validated by strain measurements of an optical fiber cantilever beam covered by Pb(Zr,Ti)O3 thick film. [ABSTRACT FROM AUTHOR]

Abstract: The influence of Mn incorporation into the Sr and Ti sites of SrTiO3 ceramics on the structure, microstructure and dielectric tunability is studied in this work. For both Sr1−x Mn x TiO3 and SrTi1−y Mn y O3 formulations, the lattice parameter, calculated from X-ray diffraction profiles, was found to decrease with increasing Mn content, but with different rates. Transmission electron microscopy analysis indicated that the solid solubility of Mn for Sr1−x Mn x TiO3 system is limited to x <3%, while scanning electron microscopy analysis revealed a marked decrease of the grain size for SrTi1−y Mn y O3 ceramic samples. The temperature range where the dielectric constant is tunable was enlarged for Sr1−x Mn x TiO3 ceramics comparing with undoped SrTiO3. A higher tunability (∼70%) and quality factor (∼6000) around 75–100K were obtained as well. It is suggested that the observed dielectric behaviour is closely related to the existence of polar microregions, formed by the introduction of Mn into the Sr site. In contrast, in SrTi1−y Mn y O3 ceramics a decrease of the dielectric tunability, following a reduction of dielectric permittivity was observed. [Copyright &y& Elsevier]

The crystalline structure of the solid solution (1−x)Pb(Fe2/3W1/3)O3–xPbTiO3 (PFW–PT) with x=0, 0.2, 0.25, 0.3, 0.35, 0.4 and 1 was analysed using X-ray diffraction (XRD) with comparative cell-refinement methods, in order to detect the change in symmetry with composition. Pure PFW shows pseudo-cubic symmetry for temperatures in the range 85–423 K. For the temperatures T=85 K and T=300 K, the solid solutions have cubic or tetragonal structures. The cell constants are functions of PbTiO3 amount. A temperature-dependent Morphotropic Phase Boundary (MPB) separating the pseudo-cubic (relaxor) and tetragonal (ferroelectric) phases might be present. The ranges of compositions for this boundary are: x<0.2 at T=85 K and x∈(0.3,0.35) for T=300 K. [Copyright &y& Elsevier]

Examines the effects of lead zirconate titanate seeds on the Pt[sub x]Pb formation during pyrolysis of lead zirconate titanate thin films. Formation of metastable intermetallic phase; Variation of thickness and stoichiometry; Assessment of the crystalline texture.

The request for extremely low-temperature and short-time sintering techniques has guided the development of alternative ceramic processing. Atmosphere-assisted FLASH sintering (AAFS) combines the direct use of electric power to packed powders with the engineering of operating atmosphere to allow low-temperature conduction. The AAFS of nanometric Potassium Sodium Niobate, K0.5Na0.5NbO3, a lead-free piezoelectric, is of great interest to electronics technology to produce efficient, low-thermal-budget sensors, actuators and piezo harvesters, among others. Not previously studied, the role of different atmospheres for the decrease in FLASH temperature (TF) of KNN is presented in this work. Additionally, the effect of the humidity presence on the operating atmosphere and the role of the compact morphology undergoing FLASH are investigated. While the low partial pressure of oxygen (reducing atmospheres) allows the decrease of TF, limited densification is observed. It is shown that AAFS is responsible for a dramatic decrease in the operating temperature (T < 320 °C), while water is essential to allow appreciable densification. In addition, the particles/pores morphology on the green compact impacts the uniformity of AAFS densification. [ABSTRACT FROM AUTHOR]

Ba 1−x Sr x TiO 3 compounds are widely recognized as leading dielectric materials for tunable electronic applications. To expand their applicability and enable integration with polymers and metals, there is a need for low-temperature processing. Here we show that Cold Sintering Process (CSP) enables the fabrication of Ba 0.6 Sr 0.4 TiO 3 (BST) tunable dielectric ceramics, using Ba(OH) 2 ·8 H 2 O as a flux, at a temperature as low as 350 ºC. A dielectric permittivity with a low magnitude of ∼ 340 at 10 kHz, an electric-field tunability of 11%, and a thermal stability of ±7.1% over the temperature range of −90 ºC to 85 ºC are obtained for CSP BST that thus outperforms conventionally sintered BST ceramics. Significant decrease in the sintering temperature and enhanced dielectric performance respond to the current sustainability concerns related to energy efficiency and tunable device requirements. [ABSTRACT FROM AUTHOR]

Up until now, no direct evidence of protein adsorption processes associated with polar activity of a piezoelectric has been reported. This work presents the experimental evidence of the protein adsorption process' dependence on the surface polarization of a piezoelectric by showing at the local scale that the process of protein adsorption is highly favored in the poled areas of a piezoelectric polymer such as poly(L-lactic) acid. [ABSTRACT FROM AUTHOR]

Observation of abnormal (against the applied electric field) domain switching in Pb(ZrxTi1-x)O3 films by piezoresponse force microscopy is reported. In some grains polarization orients opposite to the external field in the presence of the applied field, while the rest of the film volume switches in a normal way. This effect is observed in thin film capacitors which excludes charge injection effect and spontaneous backswitching due the built-in field, which is the possible reason for this behavior. The abnormal switching behavior is attributed to the charge compensation effect at the boundaries of the grains with rhombohedral structure. [ABSTRACT FROM AUTHOR]

The crystalline symmetry of the solid solution formed by a relax or and a ferroelectric material with formula: (1-x)Pb(Fe[sub 2/3]W[sub 1/3])O[sub 3]-xPbTiO[sub 3], with various x was investigated, at T = 300 K. A continuous change from pseudocubic to tetragonal symmetry, with cell parameters dependent on the PbTiO[sub 3] amount, was found. In a large range of compositions, from x = 0.20 to x = 0.37, both phases coexist, with different relative amounts. [ABSTRACT FROM AUTHOR]

Barium titanate (BT) nanoparticles were prepared using both microwave- and conventional oven-assisted hydrothermal syntheses with varying reaction times (1 h, 3 h, and 6 h). In the case of the conventional oven-assisted hydrothermal syntheses, 16 h, 24 h, 48 h and 72 h reaction times were also studied. Structural and morphological evolution of BT particles were investigated. Microwave-assisted hydrothermal synthesis allowed for the rapid formation of nearly pure barium titanate (BT) phase in just 1 h at 200 °C. On the other hand, using a conventional oven as the heat source required at least 6 h of synthesis to achieve a similar material. When the different BT powders were pelletized and sintered at 1300 °C, ceramics with over 95 % density were obtained. The room-temperature (RT) dielectric permittivity exceeded 1750 for BT particles prepared over 6 h using both heating methods. However, a significant distinction emerged when comparing the piezoelectric coefficient (d 33) values. The BT pellet obtained through the sintering of BT synthesized in the conventional oven for 6 h exhibited a notably higher d 33 value, approximately 171 pC/N, as opposed to the 146 pC/N value observed in BT ceramics resulting from the microwave synthesized powders. Among the ceramic BT variations, the one derived from the best-crystallized tetragonal BT particles (CON_72h) displayed the lowest d 33 value at 79 pC/N. These findings underscore the immense potential of microwave- and conventional oven-assisted hydrothermal syntheses in the sustainable production of BT nanomaterials, which can then be sintered to enable the preparation of ceramics with enhanced ferroelectric and piezoelectric properties. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of the synthesis and characterization of Zn1−xCoxO (0 ≤ x ≤ 0.05) nanopowders using a chemical co-precipitation approach. The structural, morphological, and vibrational properties of the resulting ZnO nanostructures were assessed through X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy to examine the influence of cobalt doping. Remarkably, a notable congruence between the experimental results and the density functional theory (DFT) calculations for the Co-doped ZnO system was achieved. Structural analysis revealed well-crystallized hexagonal wurtzite structures across all samples. The SEM images demonstrated the formation of spherical nanoparticles in all the samples. The vibrational properties confirmed the formation of a hexagonal wurtzite structure, with an additional Raman peak corresponding to the F2g vibrational mode characteristic of the secondary phase of ZnCo2O4 observed at a 5% cobalt doping concentration. Furthermore, a theoretical examination of cobalt doping's impact on the elastic properties of ZnO demonstrated enhanced mechanical behavior, which improves stability, recyclability, and photocatalytic activity. The photocatalytic study of the synthesized compositions for methylene blue (MB) dye degradation over 100 min of UV light irradiation demonstrated that Co doping significantly improves photocatalytic degradation. The material's prolonged lifetime, reduced rate of photogenerated charge carrier recombination, and increased surface area were identified as pivotal factors accelerating the degradation process. Notably, the photocatalyst with a Zn0.99Co0.01O composition exhibited exceptional efficiency compared to that reported in the literature. It demonstrated high removal activity, achieving an efficiency of about 97% in a shorter degradation time. This study underscores the structural and photocatalytic advancements in the ZnO system, particularly at lower cobalt doping concentrations (1%). The developed photocatalyst exhibits promise for environmental applications owing to its superior photocatalytic performance. [ABSTRACT FROM AUTHOR]

The dielectric response of Sr1-1.5xBixTiO3 films (0.002 ≤ x ≤ 0.167), prepared by sol-gel and deposited on Si/SiO2/TiO2/Pt substrates, is analyzed as a function of frequency and temperature. The hysteretic behavior of the polarization versus the electric field is studied as well. Between 100 Hz and 1 MHz, the real part of the dielectric permittivity &eh;′ exhibit a relaxation between ∼60 and 260 K, shifting to high temperatures with increasing the Bi content. In the imaginary part of the dielectric permittivity &eh;′′ of these films two relaxations are induced by Bi doping below the temperature of the &eh;′ relaxation. The first relaxation observed in films with 0.002 ≤ x ≤ 0.10 follows the Arrhenius law with an activation energy of U = 64-80 meV and a preexponential term τ0 = (0.3-10.8) × 10-14 s almost independent on the Bi content and is ascribed to the individual hopping of dipoles created by the off-center Bi ions. The second relaxation observed in the films with 0.04 ≤ x ≤ 0.167 is described by the Vögel-Fulcher relation with U = 2-38 meV, τ0 = 5 × 10-10-5 × 10-6 s and a freezing temperature Tf = 50-102 K, increasing with Bi content, and is attributed to the presence of polar clusters of interacting Bi ions. Slim P(E) hysteresis loops are observed at low temperatures, confirming the appearance of a polar state. The effect of Bi incorporation in ST films is qualitatively the same as the relaxorlike behavior observed in Bi-doped ST ceramics and the dissimilarities are explained based on the influence of the substrate and by a higher homogeneity of the dopant distribution in the sol-gel derived films. [ABSTRACT FROM AUTHOR]

The addition of low loss ilmenite impurities, can effectively tailor the dielectric properties of MgTiO3 without modifying the crystal structure. In the present study, the modification of the structural and dielectric properties of sol gel derived MgTiO3 films by doping with Ni and Zn is exploited. The change of the dielectric response and unit cell parameters of doped MgTiO3 is correlated with Ni and Zn occupancy. The temperature stability of MgTiO3 thin films is improved with doping, while the dielectric losses are aggravated with both Zn and Ni doping, which is correlated with the localized d electrons of the dopant cations. The dielectric permittivity decreased with Ni doping while it increased with Zn, which is attributed to the lower ionic polarizability of Ni2+ (1.23 Å3) as in comparison with Mg2+ (1.32 Å3) while Zn2+ has a higher ionic polarizability (2.04 Å3). [ABSTRACT FROM AUTHOR]

[Display omitted] • KNN dissolution in aqueous media is incongruent since lixiviated ions concentration do not comply with KNN stoichiometry. • The dissolution follows the trend [K+] > [Na+] ≫ [Nb5+]. • Acidic pH enhances KNN solubility and promotes dissolution incongruence, with ([Na+] + [K+])/[Nb5+] ratio up to 190. • Alkaline pH decreases solubility and minimizes dissolution incongruence, with ([Na+] + [K+])/[Nb5+] ratio < 10. • Temperature affects strongly [Na+]/[K+] ratio, influencing KNN dissolution incongruence especially in the alkaline pH range. K 0.5 Na 0.5 NbO 3 (KNN) is as a relevant lead-free piezoelectric material due to its piezoelectric performance and a high Curie temperature. Although high-sintering temperature is required for obtaining dense KNN ceramics, it favours alkalis volatilization with deleterious effects on the physical properties. Together with the need of more environmentally-friendly technologies for ceramic manufacturing, cold sintering (CSP), a low temperature sintering process, is a promising technique. CSP of incongruently dissolving materials (with different dissolution rates of constituents) is, however, a challenge. In this work, a systematic study of the interaction of KNN particles with water under different pH conditions and temperatures is used to elucidate the nature and mechanisms of KNN dissolution. The KNN dissolution follows the trend [K+] > [Na+] ≫ [Nb5+]. Differences are demonstrated between acidic, neutral, and alkaline conditions, with the latter exhibiting less incongruence. Acidic pH increases solubility of KNN and promotes the incongruence of dissolution. Oppositely, alkaline pH decreases solubility of KNN and prevents dissolution incongruence. The incongruence of KNN dissolution in aqueous media is quantified. These observations have implications for our understanding of powders dissolution and offer opportunities to control the stoichiometry of the powders, that might be the key for CSP of incongruently dissolving materials. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) and high-frequency dielectric properties of Li-doped KTaO 3 (K 1- x Li x TaO 3 , KLT100 x) ceramics, KLT5 and KLT10, are studied in the 15–300 K temperature range. Using the resonant microwave spectroscopy at 5.8 GHz, time-domain THz spectroscopy (∼10–40 cm−1) and far-infrared reflectivity (∼30–650 cm−1) in conjunction with the dielectric properties earlier published in the 100 Hz – 100 MHz frequency range, a broad-band dielectric response of ceramics in the whole 100 Hz – 20 THz range is obtained and compared with that recently published for KLT4.3 and KLT8 crystals. According to SHG, unlike in crystals, the ferroelectric phase transition temperature in both ceramics appears near 100 K. The dielectric soft mode softening is less pronounced, and the low-frequency permittivity increases less on cooling, when compared with crystals. The relaxational behavior below the microwave range is very similar and the main relaxations follow the same Arrhenius law as in the crystals. [ABSTRACT FROM AUTHOR]

Ultrafast high-temperature sintering (UHS) is a rapidly growing research area of material science and engineering. Herein we present UHS of gadolinia-doped ceria (GDC) powders in single and multi-step approaches. The sintered ceramics were characterized from a physical and electrochemical point of view. When the power is applied gradually during the multistep UHS process crack-free GDC ceramics can be obtained with 95 % bulk density using commercial powder. Oxalate converted GDC powder gave 86 % bulk density with the same multistep sintering process. Additionally, it is shown that multistep UHS is also suitable for multilayer co-sintering necessary for solid oxide fuel cells (SOFC), as demonstrated by the production of dense GDC electrolyte in tight contact with porous electrodes. • Ultrafast high-temperature sintering was used to prepare Gd-doped ceria ceramics. • Single and multi-step sintering cycles were developed to improve the final compacts. • Electrochemical performance of the final ceramics was studied. • Co-sintering of SOFC layered systems by UHS was successfully developed. [ABSTRACT FROM AUTHOR]

A major challenge for integration of functional oxides, such as ferroelectrics, into microelectronics and flexible electronics is the reduction of their processing temperature, which needs to be lower than the degradation temperature of silicon and flexible plastic substrates. Aiming that, attention has been given to low-temperature processing of oxide films by chemical solution deposition (CSD). In the field of ferroelectrics, potassium sodium niobate ((K 1−x Na x)NbO 3 , KNN) has aroused a special interest due to its eco-friendliness, despite the high crystallization temperature. In this work, polycrystalline KNN thin films have been fabricated for the first time at a temperature as low as 400 °C using a modified CSD process, the Seeded Photosensitive Precursor Method (SPPM). Despite this low processing temperature, monophasic and stoichiometric films with appreciable values of remnant polarization, P r ∼ 10.8 μC/cm2, and hysteretic piezoresponse are obtained. These results open a window to the direct integration of KNN films into the high-performance electronic devices. [ABSTRACT FROM AUTHOR]

In this work, we have exploited FLASH sintering as an alternative sintering process in the production of porcelain stoneware. FLASH sintering of porcelain stoneware occurred at temperatures ∼ 1020 °C, for 500 V cm-1, 2 mA mm-2 in 30 s. These conditions are significantly less severe than those typically applied in its conventional sintering, 1150–1250 °C for 1 h. Despite the reduction of time and sintering temperature, FLASH sintered samples exhibit heterogeneous microstructure and elemental distribution, with localized glassy phase formed on the positive pole. By decreasing the feldspar content, less localized glassy phase and more uniform microstructures were obtained, being of relevance the highest density and microstructure uniformity attained in the composition without feldspar. These results extend the FLASH sintering applicability and illustrate its importance for the development of alternative sintering technologies in traditional ceramic industry, that in addition may benefit from the reduction of feldspar in the porcelain stoneware production. [ABSTRACT FROM AUTHOR]

Natural polymers such as cellulose have interesting tribo- and piezoelectric properties for paper-based energy harvesters, but their low performance in providing sufficient output power is still an impediment to a wider deployment for IoT and other low-power applications. In this study, different types of celluloses were combined with nanosized carbon fillers to investigate their effect on the enhancement of the electrical properties in the final nanogenerator devices. Cellulose pulp (CP), microcrystalline cellulose (MCC) and cellulose nanofibers (CNFs) were blended with carbon black (CB), carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The microstructure of the nanocomposite films was characterized by scanning electron and probe microscopies, and the electrical properties were measured macroscopically and at the local scale by piezoresponse force microscopy. The highest generated output voltage in triboelectric mode was obtained from MCC films with CNTs and CB, while the highest piezoelectric voltage was produced in CNF-CNT films. The obtained electrical responses were discussed in relation to the material properties. Analysis of the microscopic response shows that pulp has a higher local piezoelectric d33 coefficient (145 pC/N) than CNF (14 pC/N), while the macroscopic response is greatly influenced by the excitation mode and the effective orientation of the crystals relative to the mechanical stress. The increased electricity produced from cellulose nanocomposites may lead to more efficient and biodegradable nanogenerators. [ABSTRACT FROM AUTHOR]

The orientation and grain aspect ratio, size and distribution of BaLa 4 Ti 4 O 15 (BLT) ceramics have been studied as a function of sintering temperature with a view to elucidating a general principle by which the microwave properties (MW) can be understood/tuned in systems which exhibit anisotropic grain structures. For BLT sintered at 1500 °C, ε r reaches a maximum of 51, with tan δ minimum at 0.002 and τ ε r = − 17 ppm/°C but ε r subsequently varies non-linearly as sintering temperature increases. Since ε r and τ ε r are directly proportional in the absence of a phase transition, the variation of τ ε r as a function of the sintering temperature is also nonlinear. This behaviour is related with variations in the orientation and grain aspect ratio, size and distribution with the sintering temperature and it is demonstrated that by controlling sintering conditions, microwave dielectric properties can be tuned. It is proposed that this is a general phenomenon which can also be used to explain the variation and tune the properties of other ceramic systems with anisotropic grain structures. [ABSTRACT FROM AUTHOR]

This paper describes the decay kinetics of electrically induced polarization of poly(L-lactic) acid (PLLA) via piezoresponse force microscopy. Two crystalline forms of PLLA (α and α′) were electrically poled at different temperatures (room and above glass transition). Poling at temperatures above glass transition allowed obtaining polarization stable up to 10 days for both forms. This period is enough to trigger and maintain proteins adhesion and cells proliferation, if PLLA is used as a platform for tissue growth. When poled at room temperature, both structures lose polarization after a short time (minutes to hours) being polarization in α PLLA stable for longer time. [ABSTRACT FROM AUTHOR]

Alternative sintering technologies promise to overcome issues associated with conventional ceramic sintering such as high thermal budgets and CO2 footprint. The sintering process becomes even more relevant for alkali-based piezoelectric ceramics such as K0.5Na0.5NbO3 (KNN) typically fired above 1100 °C for several hours that induces secondary phase formation and, thereby, degrades their electrical characteristics. Here, an ability of KNN ceramics to be of high performance is successfully demonstrated, using an electric field- and current-assisted Flash sintering technique at 900 °C only. Reported for the first time, Flash sintered KNN ceramics have room-temperature remnant polarization Pr = 21 μC/cm2 and longitudinal piezoelectric coefficient d33 = 117 pC/N, slightly superior to that of conventional ones due to the reduced content of secondary phases. High-performance KNN ceramics Flash sintered at a low-thermal budget have implications for the development of innovative low carbon technologies, electroceramics stakeholders, and piezoelectric energy harvesters. [ABSTRACT FROM AUTHOR]

In this article, a novel study of the design and characterization of barium strontium titanate (BST) thick films produced by electrophoretic deposition (EPD) on flexible platinum foils is reported. Intended for sub-6 GHz radio frequency (RF) applications, a study on film and electrode thickness is conducted. First, a comparison of tunability and quality factor between different film thicknesses regarding frequency is performed. The Ba0.7Sr0.3TiO3 varactors demonstrate variable capacitance between 49% and 55% for frequencies from 500 MHz to 5 GHz. Afterward, the influence of electrode thickness on the capacitance and quality factor of the films are studied. The variable capacitance and the quality factor present a tradeoff regarding the parametric studies of film and electrode thicknesses. Lastly, a microstrip line is deposited over the BST thick film to simulate and measure the phase-shifting capabilities of the device. Using a one-tone measurement setup, the small-signal S-parameter measurements of the phase shifter are also presented, and the linearity is analyzed considering two different bias voltages, 0 and 10 V. For the first time, the BST thick films fabricated by EPD process are implemented and measured in the RF regime as a metal–insulator–metal capacitor and as a phase shifter circuit. [ABSTRACT FROM AUTHOR]

Low-loss dielectrics with low sintering temperatures will facilitate microelectronics to reach the high levels of integration that wireless communications currently require. In this work the phase-formation mechanism of 1:1 Al2O3–TeO2 is proposed. It is shown that TeO2 oxidation, which occurs in air at >600°C to form Te4O9 and TeO3, triggers Al2TeO6 formation. The dielectric permittivity of Al2TeO6 was calculated to be ∼22 at 1MHz. Al2TeO6 is a promising material for ceramic bodies or substrates for dielectric applications, [ABSTRACT FROM AUTHOR]

YMnO3 is a multiferroic with a high-temperature ferroelectric phase transition (T C =913K) and a subambient Neel temperature (T N =70K). Ferroelectricity has been reported for single crystals and epitaxial thin films but to date not for ceramics. We postulate that the absence of direct evidence of ferroelectricity in ceramic YMnO3 might be attributed to microcrack formation (3.2vol.%) on cooling. We show that microcracking originates from a combination of 3.7vol.% change and strong anisotropy in the thermal expansion coefficient (α) of the hexagonal structure (αa–αc|≈4.57×10−5 °C−1) between 600 and 1000°C. [ABSTRACT FROM AUTHOR]

TiTe3O8 ceramics and films can be well sintered below 800°C and consequently have the potential to be used for low-temperature co-fired ceramics. TiTe3O8 thick films were fabricated by electrophoretic deposition on platinized Si substrates using TiTe3O8 powders synthesized by a conventional solid-state reaction. The permittivity of TiTe3O8 films is ∼54, with loss tan δ of ∼0.009, measured at 100kHz. The temperature coefficients of permittivity of TiTe3O8 films and ceramics between 35 and 200°C are +78 and −100ppm°C−1, respectively. [Copyright &y& Elsevier]

Morphology modification of ferroelectric materials at the nanoscale is an important aspect for further development of ferroelectrics. In this work, the synthesis of nanoporous barium titanate prepared under the assistance of Pluronic PE 10300 block copolymer is reported. Nanopores reside inside the BaTiO3crystallites that exhibit a specific BET surface area around 70 m2/g and nanopore volume fraction of 44.7%. X-ray diffraction of nanoporous BaTiO3indicates an average cubic structure while Raman spectra suggest local structural distortions of the lattice. With Landauer-Bruggeman effective medium approximation (LB-EMA), the dielectric constant (at 1 MHz) of nanoporous BaTiO3and solid BaTiO3(excluding all porosity) was estimated as 112 and 706, respectively, implying an effective way to manipulate the dielectric constant of materials by introducing nanopores. [ABSTRACT FROM AUTHOR]

Abstract: The effect of nonstoichiometry on the densification of SrTiO3 ceramics with Sr/Ti ratios from 0.997 to 1.02 was systematically addressed. The kinetics of densification was studied by dilatometric analysis. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for crystallographic and microstructure characterization. Ti excess enhanced matter transport during sintering whereas Sr excess decreased it. The shrinkage rate and average grain size increased with the decrease of Sr/Ti ratio. Close values of the activation energy for the initial densification and the near constant onset temperature for densification suggest that identical transport mechanisms control the densification of all the compositions. Small excesses of TiO2 and SrO were mostly incorporated into the perovskite lattice inducing alterations in the defect chemistry of the material and the mass transport during sintering is controlled by Sr vacancies. Very small stoichiometric variations have a strong influence on the sintering kinetics and resulting microstructure of ST ceramics. [Copyright &y& Elsevier]

Different macroscopic properties of PZT fibers have been obtained when using acetic acid and methacrylic acid to modify the PZT precursor. In order to clarify the role of the acids the molecular structure of the acidified PZT precursors was investigated and compared by gas chromatography-mass spectrometry, Fourier transform infrared, 13C nuclear magnetic resonance (NMR) spectroscopy (solution and solid state 13C NMR) and the reason for obtaining long PZT fibers is discussed. The results indicate that when methacrylic acid was used, long gel and ceramic fibers have been obtained because strongly co-ordinating carboxylate groups of methacrylic acid were formed. Linear chains, like those of methacrylic acid propyl ester and methacrylic acetate, have been formed in the PZT precursor sols. In addition, after heat treatment the polymer decomposed quickly so that pure perovskite could be obtained at low temperature in the PZT fibers. When acetic acid was used short fibers were obtained. Acetic acid may act as chelate agent to form oxo acetate in the precursors; this oxo acetate nature also resulted in PZT fibers drawing. However, the longest gel and ceramic fibers have been prepared from precursors with methacrylic acid. [ABSTRACT FROM AUTHOR]