Double-diffusive Marangoni convection in a rectangular cavity with horizontal temperature and concentration gradients is considered. Attention is restricted to the case where the opposing thermal and solutal Marangoni effects are of equal magnitude ͑solutal to thermal Marangoni number ratio R =−1͒. In this case a no-flow equilibrium solution exists and can remain stable up to a critical thermal Marangoni number. Linear stability analysis and direct numerical simulation show that this critical value corresponds to a supercritical Hopf bifurcation point, which leads the quiescent fluid directly into the oscillatory flow regime. Influences of the Lewis number Le, Prandtl number Pr, and the cavity aspect ratio A ͑height/length͒ on the onset of instability are systematically investigated and different modes of oscillation are obtained. The first mode is first destabilized and then stabilized. Sometimes it never gets onset. A physical illustration is provided to demonstrate the instability mechanism and to explain why the oscillatory flow after the onset of instability corresponds to countersense rotating vortices traveling from right to left in the present configuration, as obtained by direct numerical simulation. Finally the simultaneous existence of both steady and oscillatory flow regimes is shown. While the oscillatory flow arises from small disturbances, the steady flow, which has been described in the literature, is induced by finite amplitude disturbances.

Electrical fatigue tests have been conducted on PLZT ferroelectric ceramics. It was found that the higher the applied electrical field magnitude, the faster the Pr decreases; the samples under the same electrical field magnitude but with square wave have higher fatigue rate than that of sine wave. It was observed that at low frequency of applied field (50Hz and 500Hz), the polarization decreased very quickly and dropped below 70% of the original value within 106.2 switching cycles, however, when fatigue test were conducted at high frequencies of 100kHz and 300kHz, the polarization did not change significantly even after 109 cycles. The SEM analysis indicated that the facture mode was mainly of trans-granular for the virgin non-fatigued sample, while of inter-granular for the fatigue sample. The quantitative information on the 90° domain switching was measured in situ using X-ray diffraction. The effects of electrical characters on electrical fatigue behavior were explained according to the mechanism of electrical fatigue in PLZT ferroelectric ceramics.

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Bi2O3 doped (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT6) lead-free piezoelectric ceramics were fabricated by a conventional sintering technique. The effects of Bi2O3 on the piezoelectric properties and microstructures of the doped BNBT6 were investigated. X-ray diffraction analysis showed that a solid solution was formed when Bi2O3 diffused into BNBT6 lattice and the crystal structure of the sintered hybrid changed from rhombohedral to tetragonal symmetry with increasing Bi2O3 amount. Piezoelectric and dielectric properties measurements revealed that doping Bi2O3 within a certain range enhanced the piezoelectric coefficient (d33), electromechanical coupling factor (kp), relative dielectric constant (ε33 T/ε0), and dielectric loss (tanδ). When 3mol% Bi2O3 was doped, both d33 and kp of the ceramics reached their maxima, 165pC/N and 24%, respectively.

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