Masafumi Kobune

高分子型刺激応答膜は生化学や医療の分野での適用が考えられているが、熱に弱い、水や有機溶媒によって生じる膨潤からの細孔径変化、応答により膜の劣化が激しい等様々な問題が生じている。これらの問題を解決するために本研究では、表面改質した多孔質ガラスの刺激応答膜を創製し、そのpH応答性を検討した。

固体高分子形燃料電池の電解質にはパーフルオロスルホン酸系の電解質膜が使用されている。しかし、低加湿、100℃以上では著しく導電性が低下する問題がある。そのため耐熱性に優れ、無加湿・低加湿条件でプロトン導電性を有する材料が研究されている。そこで本研究では、新規のプロトン導電性材料として、ゾル-ゲル法によって、シリカ骨格中にポリビニルリン酸(PVPA)をドープさせ、有機-無機ナノハイブリッド膜を作製し、導電率を評価した。得られた膜は80℃、相対湿度90%で1×10-3S/cmの導電率を示した。また、ドープさせるPVPAを増やすと導電率も増加した。

High-density ceramics with a composition of 0.24Pb(Zn<FONT SIZE="-1">_1/3</FONT>Nb<FONT SIZE="-1">_2/3</FONT>)O<FONT SIZE="-1">₃</FONT>· 0.384PbZrO<FONT SIZE="-1">₃</FONT>· 0.376PbTiO<FONT SIZE="-1">₃</FONT> were fabricated in the sintering temperature range of 1050-1250°C by the hybrid sintering (HS) process using a 28 GHz microwave technique and hot pressing. Their physical properties were compared with those of specimens conventionally sintered (CS) at 1220°C. All the obtained HS specimens were confirmed to have the single-phase perovskite structure in the present sintering temperature range. The average grain size of the HS specimens sintered at 1100-1250°C was estimated to be around 3.1-3.8 μm; that (= 3.1 μm) of HS specimens sintered at 1100°C was larger than that (= 3.0 μm) of CS specimens. The highest electromechanical coupling factor, k<FONT SIZE="-1">_p</FONT>, reached approximately 68% in the sintering temperature range of 1130-1220°C. The remanent polarization, P<FONT SIZE="-1">_r</FONT>, and the coercive field, E<FONT SIZE="-1">_c</FONT>, of the HS specimens which exhibited a slim and rectangular P-E hysteresis loop were 44 μC/cm<FONT SIZE="-1">²</FONT> and 9 kV/cm, respectively. The highest k<FONT SIZE="-1">_p</FONT> of approximately 68% and the optimal sintering temperature of 1130°C were obtained by means of hybrid sintering.

High-density 0.5PbNi_<1/3>Nb_<2/3>O_3・0.345PbTiO_3・0.155PbZrO_3(0.5PNN・0.345PT・0.155PZ)ceramics were prepared by normal sintering with the addition of 0-3.66 mol% MnO_2 and their piezoelectric and ferroelectric properties were investigated. The effect of MnO_2 addition on significantly lowering the value of tan δ in the range of 0.37 to 0.93 mol% was proven. The lowest value (=0.37%) of tan δ was obtained in ceramics with 0.75 mol% MnO_2. Electromechanical coupling factors, k_p and k_<31>, and the piezoelectric constant, d_<31>, decreased with increasing amount of MnO_2 addition. The highest values of k_p, k_<31> and d_<31> were 0.66, 0.38 and -362 pC/N, respectively, and were obtained in the ceramics without MnO_2. The effect of MnO_2 addition on improving the value of the mechanical quality factor, Q_m, was proven in the range of 0.93 to 1.85 mol% and the improvement was around twenty times that of the sample without MnO_2. The distortion in the shape of P-E hysteresis loops for samples with MnO_2 addition suggested that oxygen vacancies formed by substituting Mn^<3+> ions for B-site ions (e.g., Ti^<4+> and Zr^<4+> ions) in the perovskite structure partially inhibited the polarization reversal in the ferroelectrics. 0.5PNN・0.345PT・0.155PZ ceramics with 0.75-0.93 mol% MnO_2 show great promise as practical materials for piezoelectric applications.