Hideki Taguchi

Fabrication of novel ZrO2(Y2O3)–Al2O3 ceramics having high strength and toughness utilising pulsed electric current pressure sintering (PECPS)

Abstract Pulsed electric current pressure sintering (PECPS) makes it possible to produce novel monolithic and composite materials with well controlled microstructure or nanostructure, which has not been realised before. ZrO2 based ceramics containing 25 mol.-%Al2O3 and 0·90–1·125 mol.-%Y2O3, i.e. ZrO2(1·2–1·5 mol.-%Y2O3)–25 mol.-%Al2O3, revealing high bending strength σb≧1 GPa and high fracture toughness KIC ≧15·5 MPa m1/2 simultaneously, have been fabricated by PECPS of cubic ZrO2 solid solution (ss) powders containing both Al2O3 and Y2O3 prepared via a sol–gel process. Tetragonal ZrO2 (t-ZrO2) phase composite ceramics sintered at 1573 to 1623 K (1300–1350°C) for 10 min under 60 MPa in Ar were composed of ∼φ200 nm grains with high relative density ≧97·5%. Transmission electron microscopy observation cleared that these mechanical properties might originate from homogeneous distribution of α-Al2O3 particles in the dense t-ZrO2 matrix; the precipitation of α-Al2O3 could be achieved by adopting the ss powders and PECPS.

Regular ArticleThe Role of Trivalent Ion in the Metal-Insulator Transition in (Nd0.1Ca0.9)(Mn1-xAlx)O3 and (Nd0.1-yCa0.9+y)MnO3

The electrical resistivity of the perovskite-types (Nd[sub 0.1]Ca[sub 0.9])(Mn[sub 1[minus]x]Al[sub x])O[sub 3] (0 [le] x [le] 0.10) and (Nd[sub 0.1[minus]y]Ca[sub 0.9+y])MnO[sub 3] (0 [le] y [le] 0.06) was measured in the temperature range 80-800 K. The concentration of the Mn[sup 3+] ion decreases with increasing x or y. In the range 0 [le] x or y [le] 0.06, these systems exhibit the metal-insulator transition. In the metallic region, dp/dT increases with decreasing concentration of the Mn[sup 3+] ion, and is not affected by the Al[sup 3+] ion. On the other hand, both the metal-insulator transition temperature (T[sub t]) and the energy gap (E[sub g]) calculated from the semiconductive region increase with decreased Mn[sup 3+] concentration, and are also affected by the Al[sup 3+] ion.

The role of trivalent ion in the metal-insulator transition in (Nd[sub 0. 1]Ca[sub 0. 9])(Mn[sub 1[minus]x]Al[sub x])O[sub 3] and (Nd[sub 0. 1[minus]y]Ca[sub 0. 9+y])MnO[sub 3]

The electrical resistivity of the perovskite-types (Nd[sub 0.1]Ca[sub 0.9])(Mn[sub 1[minus]x]Al[sub x])O[sub 3] (0 [le] x [le] 0.10) and (Nd[sub 0.1[minus]y]Ca[sub 0.9+y])MnO[sub 3] (0 [le] y [le] 0.06) was measured in the temperature range 80-800 K. The concentration of the Mn[sup 3+] ion decreases with increasing x or y. In the range 0 [le] x or y [le] 0.06, these systems exhibit the metal-insulator transition. In the metallic region, dp/dT increases with decreasing concentration of the Mn[sup 3+] ion, and is not affected by the Al[sup 3+] ion. On the other hand, both the metal-insulator transition temperature (T[sub t]) and the energy gap (E[sub g]) calculated from the semiconductive region increase with decreased Mn[sup 3+] concentration, and are also affected by the Al[sup 3+] ion.