Papers by Author: Petr Pulpan

Abstract: Barium titanate (BaTiO₃) porous ceramics were prepared by conventional sintering method, and their dielectric and piezoelectric properties were measured using 31-resonators. With decreasing sintering temperature, dielectric constant showed a maximum of 5500 at 1300 °C, while piezoelectric constant and elastic compliance increased. These resonators were developed to unimorph-type vibrators and their instantaneous electric powers were measured. As the results, the maximum electric power of 129 μW was measured for the BaTiO₃ porous ceramics sintered at 1200 °C, and this value was 20 times greater than that for dense BaTiO₃ ceramics.

Abstract: In this study, a new electric power generation measurement system was developed for piezoelectric energy harvesting using unimorph-type piezoceramics. Relationships between electric power and material constants such as d₃₃, d₃₁, g₃₁, k₃₁, e33T/e0, s₁₁^E, Q_e and Q_m were investigated using various lead zirconium titanate (Pb(Zr,Ti)O₃, PZT) ceramics with different material constants. Using the equipment, pulse-type stress was applied to unimorph-type piezoceramics. Then, optimum measurement conditions were determined. Under these conditions, the electric power for piezoelectric energy harvesting was measured as a function of the material constants. Finally, it was clarified that for piezoelectric energy harvesting using a unimorph-type device, the figure of merit was combination of the 3 kinds of material constants such as large d₃₁, small e33T/e0, and large s₁₁^E.

Abstract: Porous potassium niobate (KNbO₃, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g₃₃ constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Abstract: Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

Abstract: The conditions for strontium titanate (SrTiO3, ST) nucleation and particle growth were investigated for preparation of ST/ barium titanate (BaTiO3, BT) complex nanoparticles. The conditions with and without ST nucleation were clarified. Epitaxial growth of ST layer on the BT substrate particles was studied using both conditions. Unfortunately, the ST/BT complex nanoparticles with heteroepitaxial interface were not prepared, but a new two-step solvothermal reaction method was developed. Finally, the ST/BT complex nanoparticles without heteroepitaxial interface were successfully prepared.

Abstract: Barium titanate (BaTiO3) nanoparticles were prepared by a two-step thermal　decomposition method using barium titanyl oxalate nanoparticles of size 30 nm with and without dry-jet milling. Dry-jet milled barium titanyl oxalate nanoparticles (BTO-B) were well-dispersed whereas those without the dry-jet milling procedure (BTO-A) were partially aggregated. A heat annealing of obtained BaTiO3 nanoparticles at the same temperature resulted in crystallite sizes of the BTO-A derived BaTiO3 nanoparticles much smaller than those of the BTO-B derived. A mesoscopic particle structure analysis of revealed much thinner surface cubic layer thickness of the BTO-B derived BaTiO3 nanoparticles compared with the BTO-A derived BaTiO3 nanoparticles. This indicated the particle growth rate to be the most important parameter for the surface cubic layer thickness determination. A relationship between the surface cubic layer thickness and the particle growth rate was investigated precisely in this study.

Abstract: Barium titanate (BaTiO3, BT) – bismuth titanate magnesium oxide (Bi(Mg0.5Ti0.5)O3, BMT) solid solution system ceramics were prepared by conventional sintering method in pursuit of the enhancement of the BT Curie temperature (TC, 132 °C). Normal ferroelectric polarization vs. electric-field (P-E) hysteresis loops were observed for BT-BMT ceramics with BMT contents below 20 and above 60 molar%. On the other hand, broad P-E double hysteresis loops were observed for BMT contents from 30 to 50 molar%. The origin was investigated using synchrotron XRD measurement and Rietveld analysis. The crystal structure was assigned to ferroelectric phase with domain-pinning by certain defect structures. A modified phase diagram was proposed on the basis of the temperature dependence of the crystal structure.

Abstract: Barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method using BT and KN nanoparticles. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM), and it was confirmed that two ferroelectric phases, i.e., BT-rich tetragonal and KN-rich orthorhombic phases, always coexisted for all ceramics, which suggested that 0.5BT-0.5KN ceramics had “pseudo-morphotropic phase boundary (MPB)” structure. Thus, the control of the interface area between two phases was important to enhance piezoelectric property. Finally, their piezoelectric property was measured, and the apparent piezoelectric constant d33* increased with increasing interface area.

Abstract: Barium titanate (BaTiO3, BT) grain-oriented ceramics along [110] direction were prepared by a templated grain growth (TGG) method. The [110] oriented BT platelike particles (t-BT) were used as template particles. BT grain-oriented ceramics with higher relative density (Drel) over 95 %, high degree of orientation along [110] direction (F110) over 80 % and grain sizes around 30 µm were successfully prepared using only the template particles. The relationship between microstructures and piezoelectric constant (d33) was investigated. The higher F110 was, the higher Drel and the smaller grain size were required for enhancement of the piezoelectric properties.

Abstract: Grain-oriented barium titanate (BaTiO3, BT) ceramics were prepared by a templated grain growth (TGG) method using [110]-oriented BT platelike particles as a template and hydrothermal BT sphere particles with different particle sizes as a matrix. The degree of orientation along the [110] direction, F110, was measured using an X-ray diffraction (XRD) pattern by the Lotgering method. To obtain both a high density and a high F110, the preparation conditions were optimized as functions of matrix particle size, volume fraction of the template to the matrix, and sintering temperature. As for the results, BT grain-oriented ceramics with a high density of more than 96 % were successfully prepared despite various F110 values from 0 to 98 %. Scanning electron microscopy (SEM) revealed that their average grain sizes were always 75 µm despite various F110 values and there were no anisotropic microstructures. These grain-oriented BT ceramics were poled at 100 °C, and their piezoelectric constants d33 was measured. As for the results, the d33 values increased with increasing F110 values, and at around an F110 of 85 %, d33 reached a maximum of 788 pC/N.