Effects of annealing temperature on structure and electrical properties of sol–gel derived 0.65PMN-0.35PT thin film

0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (0.65PMN-0.35PT) thin films were deposited on Pt/Ti/SiO₂/Si substrates annealed from 550 to 700 °C using sol-gel process. The effects of annealing temperature on microstructure, insulating, ferroelectric and dielectric properties were characterized. The result reveals that 0.65PMN-0.35PT thin films possess a polycrystalline structure, matching well with the perovskite phase despite the existence of a slight pyrochlore phase. The film samples annealed at all temperatures exhibit relatively dense surfaces without any large voids and the grain size increases generally with the increase of the annealing temperature. Meanwhile, pyrochlore phase is considerably generated because of the deformation of perovskite phase caused by volatilization of Pb at an excessive high-temperature. The film annealed at 650 °C exhibits superior ferroelectricity with a remanent polarization (P_r) value of 13.31 μC/cm², dielectric constant (ε_r) of 1692 and relatively low dielectric loss (tanδ) of 0.122 at 10⁴ Hz due to the relatively homogeneous large grain size of 130 nm and low leakage current of approximately 10^-6 A/cm².     

Electrical properties of high density PZT and PMN–PT/PZT thick films produced using ComFi technology

To achieve high actuation forces in piezoelectric film actuators and transducers it is desirable to have relatively thick films. Sol-gel derived films are often limited in the maximum thickness that is obtainable due to the increased probability of cracking and delamination during processing. Composite film (ComFi) technology combines conventional sol-gel processing with ceramic powder processing to enable thick (>2 μm) ferroelectric films to be deposited onto silicon substrates at temperatures as low as 710 °C. Ten micrometre thick films have been fabricated using three different piezoelectric powders [hard doped PZT, soft doped PZT and PMN–PT(85–15)]. The resultant films have high densities with relative permittivities of 800, 900 and 1800, respectively. The d₃₃ piezoelectric coefficients were found to be lower than corresponding values for the bulk material. This has been attributed to a combination of small grain size and the clamping effects of the rigid substrate. Hysteresis loop measurements show that greater fields are required to achieve a similar degree of polarisation to that of the bulk material. This indicates that the presence of the substrate also affects the ability to pole the material so further reducing the observed piezoelectric coefficient.     

Enhancement of electrical properties in the ternary PMN–PT–PZ through compositional variation,crystallographic texture,and quenching

Ternary compositions of Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMN–PZT) piezoelectric ceramic have been investigated with an aim to optimize the electrical properties for piezoelectric applications. Quenching from temperatures above the Curie point was proved to enhance the properties up to two folds in the 0.40PMN–0.25PZ–0.35PT composition. This enhancement is believed to have arisen as a result of the freezing of defect dipoles in their random distribution, and thus prevention of their domain pinning effect. Texturing the optimum composition using BaTiO₃ template particles through templated grain growth process and quenching the textured ceramic led to further enhancement with piezoelectric charge coefficient increasing from 190 to 750 pC/N, relative permittivity increasing from 860 to 1815 and remanent polarization increasing from 16 to 30 μC/cm².     

Influence of hafnium oxide on the structure and properties of powders and ceramics of the YSZ–HfO2 composition

Using the X-ray diffraction, internal friction, 4-point bending, and electron microscopy methods we have studied the structural compatibility and influence of Y₂O₃ and HfO₂ dopants addition on the structure and phase composition of ZrO₂ powders and ceramics based on them. The mechanical properties of ZrO₂–Y₂O₃-HfO₂ (YSZ) system have been investigated.It was determined that the similarity of the structure and properties of yttrium and hafnium oxides is not complete. The individual structural features of ZrO₂, Y₂O₃, and HfO₂ oxides reviled themselves during the formation of ternary systems of the YSZ-Hf type. Studies of the nY₂O₃–ZrO₂ - mHf₂O₃ system in the range of hafnium amount from 1 to 15 wt% and yttrium oxide concentration from 0 to 12 mol% showed the possibility of increase in the values of physical and mechanical properties of common two-component zirconium ceramics by the forming ternary systems of the YSZ-Hf type.     

Electrocaloric and pyroelectric properties of PZT and PMN–PNN–PZT thin films

The electrocaloric effects (EC) of PZT and PMN–PNN–PZT films were evaluated. PZT and PMN–PNN–PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN?PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN–PNN–PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN–PNN–PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated.     

Sol–gel derived PMN–PT thick films for high frequency ultrasound linear array applications

A 12-µm PMN–PT [0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃] thick film was produced by alternate spin-coating of a ceramic powder/sol–gel composite and infiltration of the sol–gel. Using this technique, a high quality PMN–PT thick film was obtained, showing a permittivity ε_r of ~3300 and dielectric loss factor of ~0.02 at 1 kHz. Photolithographic and wet etching techniques were used to fabricate a 32-element linear array from the film. The completed array showed a center frequency of approximately 110 MHz and a bandwidth of 60% at ?6 dB without a matching layer. The performance of the kerfless array was studied and compared to a kerfed array simulated with finite element analysis.     

Influence of intercalated organoclay on the phase structure and physical properties of PTT–PTMO block copolymers

Poly(trimethylene terephthalate-block-tetramethylene oxide) (PTT–PTMO) copolymer/organoclay nanocomposites were prepared by in situ polymerization. They showed an intercalated silicate structure, as determined by X-ray diffraction and transmission electron microscopy. The influence of intercalated organoclay on the two-phase structure and mechanical properties of PTT–PTMO block copolymer was examined by using DSC and tensile tests. The DSC results imply that the silicate layers (Nanofil 32) in PTT–PTMO act as nucleation agents and accelerate the crystallization of PTT hard phase during the cooling down process from the melt. The introduction of silicate layers does not have great effect on the glass transition temperature of PTMO-rich soft phase, melting temperature of PTT hard phase, and degree of crystallinity of the nanocomposites. As the organoclay loading in the nanocomposites increase, the enhanced tensile modulus and yield stress was observed. The cyclic tensile tests showed that obtained nanocomposites have values of permanent set comparable to the neat PTT–PMO copolymer.     

Influence of processing parameters on the electrical response of screen printed SrFe0.6Ti0.4O3−δ thick films

A screen printing ink of SrFe_0.6Ti_0.4O_3?δ (STFO60) nanopowders produced by Self-propagating High-temperature Synthesis (SHS) was used to produce gas sensors with high level of reproducibility at low cost. The stability and rheology of the produced ink were studied in order to obtain high quality, highly reliable films. The electrical characteristics of the sensors as a function of the firing temperature and thickness of the sensing layer were investigated. The best results were obtained stabilizing the powder with lauric acid. Laboratory bench and on-road oxygen tests demonstrated that the response of 30 μm STFO60-based resistive sensors is comparable with the one of a commercial oxygen probe.     

Low temperature preparation and electrical properties of sodium–potassium bismuth titanate lead-free piezoelectric thick films by screen printing

Sodium–potassium bismuth titanate (NKBT) thick films with thickness of 40 μm were prepared by screen printing. To improve the homogeneity, the sintering aids were added into the pastes as a chemical liquid-phase doping method. The results show that the addition of Bi–Li sintering aids was beneficial for both the reduction of the sintering temperature and the improvement of the electrical performance of the thick films. The thick films containing 5 wt.% Bi–Li sintering aids demonstrated optimal dielectric properties with the maximum dielectric constant of 725 and minimum dielectric loss of 2.5%. Moreover, the NKBT thick films containing 3 wt.% Bi–Li sintering aids sintered at 950 °C exhibited the remanent polarization of 19.6 μC/cm², room-temperature pyroelectric coefficient of 1.56 × 10^?4 C/(m² °C), figure of merit for specific detectivity of 0.48 × 10^?5 Pa^?0.5, and effective longitudinal piezoelectric coefficient of 88 pm/V, which are comparable to that of the high-temperature sintered thick films without sintering aids.     

Effect of tungsten doping on the dielectric response of PZN–PT–BT ceramics with the morphotropic phase boundary composition

In this paper, effect of tungsten doping on the dielectric property of the Pb(Zn_1/3Nb_2/3)O₃–BaTiO₃–PbTiO₃ system around morphotropic phase boundary(MPB) composition is presented. Samples were prepared according to the formula Pb_0.85−xBa_0.15[(Zn_1/3Nb_2/3)_0.7Ti_0.3]_1−xW_xO₃ assuming the compensation for W is achieved via the appearance of the lead vacancies. X-ray diffraction results show that a nearly complete perovskite phase was maintained as W was progressively added up to 5 wt.%. Introduction of W stabilizes the tetragonal phase against the rhombohedral one, resulting in the displacement of MPB composition region towards relaxor end. Moreover, lattice distortion of the tetragonal phase is enlarged, that of the rhombohedral phase is lowered. W- doping leads to an increase in the dielectric permittivity maximum and a decrease in the phase transition temperature (T_m). The frequency dispersion of T_m is succesively weakened as W ions are gradually incorporated, reflecting the strengthened couplings among ferroactive oxygen octahedra. A maximum on the degree of diffuse phase transition is observed at 1 mol% WO₃, which can be interpreted in terms of competing effects of chemical inhomogeneity and ferroelectric couplings. W-doping also induces an increase in the tendency towards Curie–Weiss behavior above T_m, which is associated with the growth of ferroelectric domains.     

Structural and electrical properties of sol–gel-derived Al-doped bismuth ferrite thin films

Al-doped BiFeO₃ (BiFe_(1?x)Al_xO₃) thin films with small doping content (x=0, 0.05, and 0.1) were grown on Pt(111)/TiO₂/SiO₂/Si substrates at the annealing temperature of 550 °C for 5 min in air by the sol–gel method. The crystalline structure, as well as surface and cross section morphology were studied by X-ray diffraction and scanning electron microscope, respectively. The dielectric constant of BiFeO₃ film was approximately 71 at 100 kHz, and it increased to 91 and 96 in the 5% and 10% Al-doped BiFeO₃ films, respectively. The substitution of Al atoms in BiFeO₃ thin films reduced the leakage current obviously. At an applied electric field of 260 kV/cm, the leakage current density of the undoped BiFeO₃ films was 3.97×10^?4 A/cm², while in the 10% Al-substitution BiFeO₃ thin films it was reduced to 8.4×10^?7 A/cm². The obtained values of 2P_r were 63 μC/cm² and 54 μC/cm² in the 5% and 10% Al-doped BiFeO₃ films at 2 kHz, respectively.     

Influence of the ice front velocity and of the composition of suspensions on thermal properties of bentonite materials prepared using freeze–casting process

The influence of (i) the ice front velocity in the freeze–casting process as well as the addition of two binders, (ii) the inorganic synthetic mineral laponite and (iii) the natural organic oligomer chitosan, on the microstructure and on thermal conductivity of bentonite materials prepared using the freeze–casting process were investigated by scanning electron and interferometric microscopies and the laser flash method. Prior to measurements, materials physico-chemical characteristics were determined using specific surface area, grain size and density measurements. Results show that the width of the strongly oriented pores obtained with the freeze–casting process is modified by the presence of binders, and that in turn, the thermal conductivity and anisotropy are also significantly modified.     

Influence of substrate composition on corrosion protection of sol–gel thin films on magnesium alloys in 0.6 M NaCl aqueous solution

The corrosion protection behaviour of organic–inorganic hybrid thin films on AZ31 and AZ61 magnesium alloy substrates has been studied. These films were prepared by a sol–gel dip-coating method. The organopolysiloxane precursors were γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethoxysilane (TMOS). An attempt was made to determine the possible relationships between the degradation of the sol–gel film and composition of the metal substrate during the exposure of the metal/coating system to 0.6 M NaCl aqueous solutions. For this purpose electrochemical impedance spectroscopy (EIS) and hydrogen evolution measurements were applied. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the sol–gel films formed on the surface of AZ61 alloy were far more perfect and uniform than those formed on the AZ31 alloy. This behaviour was attributed to the effect of the native oxide film initially present on the surface of the AZ61 alloy, which inhibited the attack of magnesium. Results indicated that the sol–gel coated AZ61 substrate tended to develop corrosion products slower than the sol–gel coated AZ31 substrate, trend that could change by prolonging exposure time. After 6 days of immersion, a clear inhibitive effect of the corrosion products formed during the test was observed in the case of the sol–gel coated AZ31, but not with the coated AZ61 alloy substrate, a phenomenon explained by the carbonate enrichment observed by XPS.     

The effect of the surface nanostructure and composition on the antiwear properties of zirconia–titania coatings

This study describes the preparation, surface imaging and tribological properties of titania coatings modified by zirconia nanoparticles agglomerated in the form of island-like structures on the titania surface. Titania coatings and titania coatings with embedded zirconia nanoparticles were prepared by the sol–gel spin coating process on silicon wafers. After deposition the coatings were heat-treated at 500 °C or 1000 °C. The natural tendency of nanoparticles to form agglomerates was used to build separated island-like structures unevenly distributed over the titania surface having the size of 1.0–1.2 μm. Surface characterization of coatings before and after frictional tests was performed by atomic force microscopy (AFM) and optical microscopy. Zirconia nanoparticles were imaged with the use of transmission electron microscopy (TEM). The tribological properties were evaluated with the use of microtribometer operating in ambient air at technical dry friction conditions under normal load of 80 mN. It was found that nanocomposite coatings exhibit lower coefficient of friction (CoF) and considerably lower wear compared to titania coating without nanoparticles. The lowering of CoF is about 40% for coatings heated at 500 °C and 33% for the coatings heated at 1000 °C. For nanocomposites the wear stability was enhanced by a factor of 100 as compared to pure titania coatings. We claim that enhanced tribological properties are closely related to the reduction of the real contact area, lowering of the adhesive forces in frictional contacts and increasing of the composite hardness. The changes in materials composition in frictional contact has secondary effect.     

Effects of vanadium and manganese concentrations on the composition,structure and electrical properties of ZnO-rich MnO2–V2O5–ZnO varistors

The composition, structure and electrical properties of ZnO-rich MnO₂–V₂O₅–ZnO varistors have been analysed. Samples were prepared by a conventional powder route with 0.25–0.75 V₂O₅ mol% and 0.1–1.5 MnO₂ mol% concentrations. All the microstructures consisted of ZnO grains with zinc vanadates as minority secondary phases. The quantity and type of zinc vanadates found depended on the cooling rate. α-Zn₃(VO₄)₂ and Zn₄V₂O₉ were found in air-cooled samples, whereas γ-Zn₃(VO₄)₂ and Zn₄V₂O₉ were found in samples cooled relatively slowly at 5 °C min⁻¹. All samples exhibited non-linear current-voltage varistor behavior, with non-linear coefficients, α, ranging from 9.7 to 27.3. The electrical behaviour was relatively insensitive to the different rates of cooling. The highest values of α were obtained in slowly cooled samples when the MnO₂ concentration was 0.25 mol% and when the V₂O₅ concentration was 0.5 mol%.     

Influence of the sintering conditions on the properties of 0.57PSN–0.43PT ceramics prepared from mechanochemically activated powder

The present work is a systematic study of the influence of the sintering conditions on the structural and electrical properties of 0.57Pb(Sc_1/2Nb_1/2)O₃–0.43PbTiO₃ ceramics prepared from mechanochemically activated powder. The ceramics were sintered at various temperatures and for a range of times. Three or even more contributions competed for influence on the functional properties of the ceramics, i.e., the density, the grain size and the phase composition. However, all these contributions combined in such a way that the best functional properties were obtained for the ceramics sintered at 1000 °C for 8 h.     

Influence of La3+ additions on the phase behaviour and antibacterial properties of ZrO2–SiO2 binary oxides

The present study reports the influence of lanthanum (La³⁺) content on the phase stability and antibacterial activity of ZrO₂–SiO₂ binary oxides. Four different concentrations of La³⁺ additions in ZrO₂–SiO₂ binary oxides were synthesized using a sol–gel technique. Heat treatment of the synthesized powders resulted in the formation of t-ZrO₂ phase at 1000 °C. Heat treatment beyond 1000 °C resulted in the phase degradation of t-ZrO₂ to yield m-ZrO₂ and ZrSiO₄. Results from antibacterial tests confirmed the potential activity of La³⁺ doped ZrO₂–SiO₂ binary oxides in countering the microbial invasion.     

Effect of clay dispersion methods on the mechano-dynamical and electrical properties of epoxy–organoclay nanocomposites

The effect of different clay dispersion methods on the mechano-dynamical and electrical properties of epoxy/clay nanocomposites was investigated. Three different clay dispersion methods (high-speed mechanical shearing, ultrasonication (US), and an optimal combination of high-speed shearing and US) were used for the dispersion of the clay in the epoxy resin. 3 wt% of an organoclay, cloisite 30B, was used as the nanoclay. Wide-angle X-ray diffraction technique and electron microscopic techniques (SEM and TEM) were used to study the morphology of the nanocomposites. Dynamic mechanical analysis was used to study the dynamo-mechanical properties. Studies on the dielectric breakdown strength (EBD) of the nanocomposites show that the EBD strongly depends on the clay dispersion time and clay dispersion method. Pulsed electro-acoustics method measurement shows that the space charge accumulation was considerably reduced in the nanocomposites. In particular, reduction in space charges after polarization depends on the dispersion of the nanofillers, the better the degree of dispersion, the lower the space charges observed.     

Influence of SPS temperature on the properties of TiC–SiCw composites

Titanium carbide (TiC) composites containing 10 vol% silicon carbide whisker (SiC_w) were spark plasma sintered at different temperatures of 1800, 1900, and 2000 °C under a pressure of 40 MPa and a holding time of 7 min. At the sintering temperature of 1900 °C, the relative density, Vickers hardness, and flexural strength of the sintered samples hit their maximum values of 98.7%, 24.4 GPa, and 511 MPa, respectively. The microstructural characteristics of the sintered samples were assessed by optical and field emission scanning electron microscopy (FESEM) and XRD. The results revealed that at 1900 °C, the dispersion of SiC_w in the TiC matrix was homogenous, no chemical reaction took place between the reinforcement and the matrix, and produced a fine-grained microstructure. It was found that the thermal conductivity of SPSed samples did not have the same trend with relative density and mechanical properties. A maximum value of 32.3 W/mK was measured for the thermal conductivity of the composite sintered at 2000 °C.