Q.F Zhou

PZT ceramic/ceramic 0–3 nanocomposite films for ultrasonic transducer applications

Abstract Lead zirconate titanate (PZT) ceramic/ceramic 0–3 nanocomposite films of several micron thickness were fabricated using a modified sol–gel process. Nanosized PZT powder was dispersed in a PZT solution which was spin-coated onto stainless steel or silicon substrates to form composite films. The crystallization of the films was studied by X-ray diffraction. The dielectric permittivities and ferroelectric properties of the PZT films deposited on stainless steel substrates were also investigated.

Characterization of barium titanate ceramic/ ceramic nanocomposite films prepared by a sol-gel process

Abstract Barium titanate (BaTiO 3 ) ceramic/ceramic nanocomposite thick films (∼16μm) for ultrasonic transducer applications were prepared by a modified sol-gel process. Nano-sized BaTiO 3 powder was dispersed in a sol-gel matrix of BaTiO 3 to form a composite solution. Films were prepared by spin coating and then annealed at various temperatures. The crystallization of the composite film was studied by X-ray diffraction. The dielectric permittivity and the ferroelectric properties of the film were also measured.

Nanocrystalline powder and fibres of lead zirconate titanate prepared by the sol-gel process

Abstract Nanocrystalline powder and fibres of lead zirconate titanate (PZT) were prepared by the sol-gel process. The structural variation of the PZT powder with annealing temperature was studied by differential thermal analysis, thermogravimetry and x-ray diffraction. The lowest temperature for the formation of single-phase PZT nanocrystals in the powder was found to be 650°C and the average crystallite diameter in the powder annealed at 650°C was 35 nm. By controlling the concentration of the precursor, fibres of diameter 50–100 μm were drawn from the gel. After annealing at 700°C the crystallite size in these fibres was 0.3 – 0.5 μm.

Synthesis and properties of ferroelectric SrBi2Ta2O9 powder and films prepared by a sol–gel process

Crystalline powder with particle size <200 nm and films with thickness <350 nm of SrBi 2 Ta 2 O 9 (SBT) with a layered perovskite structure were prepared by a sol-gel technique using an alkoxide-carboxylate precursor solution. The structural variation of the SBT powder with annealing temperature was studied by thermogravimetry (TGA), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffractometry (XRD). The lowest temperature for the formation of a pure perovskite phase of SBT was found to be 650°C. The average crystallite diameter in the films annealed at 650°C was 70 nm. The ferroelectric hysteresis loop of the SBT films was also obtained.

Raman spectra and structural phase transition in nanocrystalline lead lanthanum titanate

The effects of particle size on the structure and Raman spectra of lead lanthanum titanate nanocrystalline particles are investigated. Samples with different particle sizes were prepared by the sol–gel process using different calcination temperatures. The sizes of the crystallites of particles were determined by x-ray diffraction with the aid of Scherrer’s equation. Raman vibration modes of samples with various particle sizes were also studied by Raman scattering at room temperature. The results show that the tetragonal distortion of the unit cell apparently decreases with decreasing particle size: the soft A1(1TO) phonon mode which is related to the spontaneous polarization of ferroelectric materials shifts toward lower frequency, and other peaks exhibit broadening and intensity changes with decreasing particle size. These are attributed to a phase transformation from the ferroelectric tetragonal to the paraelectric cubic phase. The above phenomena are related to a grain size-induced structural phase tra...

Nanocomposite ultrasonic hydrophones

Abstract Needle-type hydrophones for the calibration of medical ultrasonic transducers have been fabricated using lead zirconate titanate (PZT)/poly(vinylidene fluoride-trifluoroethylene) (PZT/P(VDF-TrFE)) 0–3 nanocomposite films. The 0–3 nanocomposite film has been prepared by incorporating nanosized PZT powder (derived from a sol–gel process) in a P(VDF-TrFE) matrix. Since the piezoelectric coefficients of PZT and P(VDF-TrFE) have opposite signs, the PZT and P(VDF-TrFE) phases in the nanocomposites have been poled in opposite directions in order to give enhanced piezoelectric activity. A nanocomposite hydrophone with 0.2 volume fraction of PZT has been characterized and found to be more sensitive than a P(VDF-TrFE) hydrophone of similar structure.

Conducting lanthanum nickel oxide as electrodes for lead zirconate titanate films

Abstract Lanthanum nickel oxide (LaNiO3 or LNO) is a conducting ceramic which has good potential for use as electrodes in multilayer actuators. In this work, lead zirconate titanate (PZT) films were prepared by a modified sol–gel process on stainless steel substrates. A LNO film prepared by a metal–organic deposition method was spin-coated onto the PZT film and the LNO/PZT film was cofired by rapid thermal processing at various temperatures. A transition layer consisting of a mixture of PZT and LNO was introduced between the LNO and PZT layer in order to enhance adhesion. The electrical resistivity of the LNO films was measured as a function of the sintering temperature and 750°C was found to be the optimum sintering temperature. The microstructures of the LNO/PZT films were studied in a scanning electron microscope (SEM).

High electrostriction and relaxor ferroelectric behavior in proton-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer

Effect of proton irradiation on poly(vinylidene fluoride-trifluoroethylene) 56/44 mol % copolymer has been studied using a Mach–Zehnder heterodyne interferometer, polarization hysteresis loop and dielectric constant measurements. The electrical-field-induced strain response of the copolymer after proton bombardment follows a quadratic electrostriction relationship. The electrostrictive coefficient at 5 kHz is similar to that obtained with a bimorph-based strain sensor, but at a much lower electric field. The polarization hysteresis after proton irradiation is reduced considerably and the dielectric constant exhibits typical relaxor behavior, which is suggested as the cause of the observed results.

Effects of dispersing agent on the microstructure and properties of PCLT/P(VDF-TrFE) 0–3 nanocomposites

Abstract Powder agglomeration is a major problem in the fabrication of calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0–3 nanocomposites. To ensure uniform dispersion of the nanocrystalline PCLT powder in the P(VDF-TrFE) matrix, the powder is often dispersed in a liquid (e.g. methyl-ethyl ketone) placed in a high power ultrasonic bath. In this study, PCLT nanocrystalline powder derived from a sol-gel process was dispersed in various liquids placed in an ultrasonic bath for different periods of time tu. The size and specific surface area of the particles were measured as functions of tu. By choosing a good dispersing agent and an appropriate t, PCLT/P(VDF-TrFE) nanocomposites with a uniform dispersion of nanosized particles can be prepared. The dielectric, piezoelectric and pyroelectric properties of these composites have been investigated.

PROPERTIES OF PCLT/P(VDF-TRFE) 0-3 NANOCOMPOSITES

Abstract Calcium and lanthanum modified lead titanate (PCLT) powder with size in the nanometer range was prepared using a sol-gel technique. PCLT powder annealed at 850°C was incorporated into a polyvinylidene fluoride/trifluoroethylene P(VDF-TrFE) copolymer matrix to form 0.15 mm thick films of 0–3 nanocomposites with ceramic volume fraction (φ) ranging from 0.05 to 0.33. The dielectric and pyroelectric properties of the composites were measured as functions of temperature. The observed permittivity and dielectric loss were found to agree with the predictions of the Bruggeman model. When the ceramic and copolymer phases in these nanocomposites are poled in the same direction, the pyroelectric activities of the two phases reinforce while the piezoelectric activities partially cancel, thereby minimizing the vibration-induced electrical noise in pyroelectric current measurements.