Takeyuki Kikuchi

In this paper, we introduced the fabrication of β-TCP/Ti composites as biomaterials by the spark plasma sintering (SPS) method, and two studies to customize powders for the metal-ceramic composite (MCC) fabrication using SPS. In the study attempting the fabrication of β-TCP/Ti composite by SPS, the difficulty of metal-ceramics sintering was revealed; the decomposition of β-TCP due to the reaction with Ti particles during sintering decreased in sinterability. Thus, based on the simple strategy of “reducing the contact area between Ti particles and β-TCP particles to suppress the decomposition of β-TCP during sintering”, we attempted to solve the problem by customizing powders for the composite with two different powder preparation methods: the homogeneous precipitation method to control the agglomerate size of β-TCP, and the mechanical milling method to prepare Ti-Mg powder.

A monoclinic ferroelectric phase with the space group Pm has been discovered in lead-free (Na<inf>0.5</inf>K<inf>0.45</inf>Li<inf>0.05</inf>)NbO<inf>3</inf>solid solution ceramics synthesized by a malic acid complex solution method. At ambient temperature, the lattice parameters of this monoclinic structure were [Formula: see text]. The average and local structures of this monoclinic phase were analyzed by synchrotron X-ray measurements. The average structure maintained the monoclinic structure down to 20 K, although the local structure changed below room temperature. The distinct short-range order structure was found to be rhombohedral. The results demonstrate the presence of an order–disorder-type phase transition structurally bridging between the rhombohedral local structure and the low-symmetry monoclinic average structure in a (Na<inf>0.5</inf>K<inf>0.45</inf>Li<inf>0.05</inf>)NbO<inf>3</inf>solid solution system.

Ferromagnetic magnetite (Fe<inf>3</inf>O<inf>4</inf>) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi<inf>3.25</inf>Nd<inf>0.65</inf>Eu<inf>0.10</inf>)Ti<inf>3</inf>O<inf>12</inf>(BNEuT)/(101) Nb:TiO<inf>2</inf>substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe<inf>3</inf>O<inf>4</inf>/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe<inf>3</inf>O<inf>4</inf>with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400–420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76–89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment–magnetic field curves for Fe<inf>3</inf>O<inf>4</inf>thin films deposited at 400–500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

<p>To develop high-performance materials for high-power piezoelectric applications, ternary high-density solid solutions with compositions of xPb(Zr_0.52Ti_0.48)O₃−yPb(Mn_1/3Sb_2/3)O₃−zPb(Zn_1/3Nb_2/3)O₃ (PZT_xPMS_yPZnN_z) with x = 0.82−0.96, y = 0.02−0.16, and z = 0.02−0.16, were fabricated by a conventional solid-state reaction method. A detailed investigation was carried out into the microstructure and crystal structure of the samples, together with their piezo- and ferroelectric properties. It was found that a solid solution with x = 0.86, y = 0.085, and z = 0.055 and a rhombohedral structure exhibited excellent piezo- and ferroelectric properties. These included piezoelectric coefficients d₃₃ (longitudinal length mode) = 170 pC/N and -d₃₁ (transverse length mode) = 69 pC/N, a mechanical quality factor Q_m(p) (radial mode) = 2218, d₃₃⋅Q_m(p) = 376×10³ pC/N, -d₃₁⋅Q_m(p) = 133×10³ pC/N, electromechanical coupling factors k_p (radial mode) = 46% and k₃₁ (transverse length mode) = 28%, a Curie temperature T_c = 259℃ a remanent polarization 2P_r = 53 μC/cm², and a coercive field 2E_c = 34 kV/cm. Thus, this is a highly promising piezoelectric material for high-power ultrasonic vibrators and piezoelectric transformers.</p>

<p>(Na_0.50K_0.45Li_0.05)NbO₃ (NKLN) powder was synthesized by the malic acid complex solution method, and NKLN solid solutions were then fabricated at firing temperatures of 900−1050℃ using a conventional solid-state reaction technique. The piezoelectric properties of the resulting materials were measured, and samples produced at 950℃ were found to exhibit the maximum d₃₃ and k_p values of 151 pC/N and 32%, respectively. On the basis of a local structural analysis using high-energy X-ray diffraction, the distortion of NbO₆ octahedra, which is the origin of the ferroelectric properties, also exhibited a maximum at 950℃. Thus, this is the optimal firing temperature for fabricating NKLN samples with excellent piezoelectric properties and the largest NbO₆ octahedral distortion.</p>

We have prepared Carbon/Fe-Ni-Cu ternary alloy composites by polymerized complex method. A single-phase Fe-Ni-Cu alloy could be obtained in carbon matrix by controlling pH of the citrate complex solution. It was revealed that the chemical compositions of metals in composites were maintained well by adding ethylene glycol into the complex solution. Crystallinity of both carbon matrix and Fe-Ni-Cu alloy particles were enhanced with increasing the carbonized temperature. The composite carbonized at 700°C had larger saturation magnetization and smaller coercivity than that carbonized at 500°C, which correlated with metal content and crystallite size of alloy. The composite carbonized at 700°C exhibited larger permeability and permittivity than carbon/Fe-Co alloy composites at frequency of GHz range.

We have prepared Carbon/Fe-Ni-Cu ternary alloy composites by polymerized complex method. A single-phase Fe-Ni-Cu alloy could be obtained in carbon matrix by controlling pH of the citrate complex solution. It was revealed that the chemical compositions of metals in composites were maintained well by adding ethylene glycol into the complex solution. Crystallinity of both carbon matrix and Fe-Ni-Cu alloy particles were enhanced with increasing the carbonized temperature. The composite carbonized at 700&amp;deg;C had larger saturation magnetization and smaller coercivity than that carbonized at 500&amp;deg;C, which correlated with metal content and crystallite size of alloy. The composite carbonized at 700&amp;deg;C exhibited larger permeability and permittivity than carbon/Fe-Co alloy composites at frequency of GHz range.