M. F. Besser

High temperature phases in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic

The phase evolution with temperature in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic was investigated with dielectric permittivity and polarization measurements, hot stage transmission electron microscopy, and high temperature x-ray diffraction. Below 190 °C, the ceramic is in the antiferroelectric phase with characteristic 14{110}c superlattice diffractions. In this stage, typical antiferroelectric 180° domains were observed. Between 190 and 220 °C, an intermediate phase, which is characterized by 12{110}c-type superlattice diffractions, was detected. Evidences are found to suggest that this intermediate phase is ferroelectric. The 12{110}c-type superlattice diffraction persists even into the paraelectric phase above 220 °C. In addition, there exists an incommensurate phase between the low temperature antiferroelectric phase and the intermediate ferroelectric phase.

Structure and properties of (1 -x)Pb(Mg1/2W1/2) O3 -xPb(Zr0.5Ti0.5)O3 solid solution ceramics

The widely used piezoelectric Pb(Zr1−xTix)O3 ceramics have been known to have Zr4+ and Ti4+ randomly distributed on the B-site lattice in the ABO3 perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg1/2W1/2)O3 and the ferroelectric order in Pb(Zr0.5Ti0.5)O3 leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, Tm, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.

Quasicrystal formation in Zr-Cu-Ni-Al-Ta metallic glasses and composites

We have examined the crystallisation behaviour of Zr-Cu-Ni-Al-Ta metallic glasses and metallic-glass-matrix composites. Monolithic and composite alloys were prepared by varying the amount of Ta added to a Zr-based glass-forming alloy. We find that additions as low as 2 at.% Ta promotes the formation of the icosahedral phase during devitrification, which in turn has a significant effect on the subsequent crystallisation behaviour. The DSC and time-resolved X-ray scattering results show that following the nucleation of the quasicrystals the alloys exhibit an exothermic event that does not correspond to any discernible structural change. We discuss the possible mechanisms for the second exotherm.

Functionally gradient superconducting foils by plasma spraying

Functionally gradient composite foils of Y–Ba–Cu–O and silver with a layer thickness of around 100 μm and certain flexibility, were produced by air plasma spraying. The superconducting phase is formed in sprayed composite foils only after annealing in flowing oxygen above 900 °C but can be improved by annealing first in argon at 850 °C prior to the oxygen annealing. The effect of argon pre-treatment was found to increase the grain size of YBa2Cu3O7-δ. The behaviour of the graded silver layer in improving the ductility and in the process of recovery of superconductivity of the sprayed coating was investigated.

Structure and properties of (1 − x

The widely used piezoelectric Pb(Zr1−xTix)O3 ceramics have been known to have Zr4+ and Ti4+ randomly distributed on the B-site lattice in the ABO3 perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg1/2W1/2)O3 and the ferroelectric order in Pb(Zr0.5Ti0.5)O3 leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, Tm, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.

Structure and properties of (1 − x )Pb(Mg 1/2 W 1/2 )O 3 − x Pb(Zr 0.5 Ti 0.5 )O 3 solid solution ceramics

The widely used piezoelectric Pb(Zr1−xTix)O3 ceramics have been known to have Zr4+ and Ti4+ randomly distributed on the B-site lattice in the ABO3 perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg1/2W1/2)O3 and the ferroelectric order in Pb(Zr0.5Ti0.5)O3 leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, Tm, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.