We report on the observation of an orthorhombic ferroelectric phase in 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals, whose polarization is along 〈011〉 direction and stability can be altered by poling conditions. We studied the piezoelectric properties on poled 〈011〉 crystals, in both monodomain and polydomain states, and found that the piezoelectric d32 coefficient, which is the piezoelectric response in perpendicular to the poling direction, is positive in both cases. Based on the phenomenological theory, we show that this is possible in a crystal with the electrostrictive coefficients Q11>Q44–Q12.
may cause power blackouts. [1] Moreover, the refrigerant gases used in air conditioners are one of the largest contributors to greenhouse gas emissions. [2] Passive cooling, e.g., cooling with no power input and without greenhouse gas emission, provides an attractive solution to alleviate the power demands as well as negative environmental impact of building cooling. Recent theoretical and experimental demonstrations of subambient daytime radiative cooling (SDRC) represent a breakthrough in realizing passive daytime cooling. [3-21] These radiative cooling materials exploit the infrared transparency window of the atmosphere, in the wavelength range of 8-13 µm, to directly transmit heat from an object at ambient temperature, through blackbody radiation, to the cold outer space which has a temperature of 3 K (−270 °C). This radiation effect, in fact, is what causes one to feel chilly when staying outside in summer nights. However, to generate subambient daytime cooling under direct sunlight using the same effect, the materials must overcome the heating generated by the direct sunshine. In
We study the finite-size effect on the dispersion relation, group velocity, and transmission curves of one-dimensional finite-size coupled-resonator optical waveguide (CROW) structures. Both the dispersion relation and the group velocity curves of a finite-size CROW oscillate along those of the corresponding infinite-extended ones. The oscillations can be suppressed by matching the equivalent admittance of the surrounding medium to that of the unit cell. Thelen's method is used to find the parameters of the matching layer to reduce oscillations on the group velocity and transmission spectra, and to analyze the structure parameters that determine the bandwidth and the group velocity.
The article presents the results of a recent investigation on the ultrasonic performance of 1-3 piezocomposites. Using a guided wave approach, the electromechanical properties of the thickness resonance are modeled and the results are compared with the experimental data. The influence of various losses in a 1-3 composite on the dispersion curves and the quality factor for the thickness mode is examined. It is found that the reduction in the quality factor of a composite compared with piezoceramic is mainly due to the acoustic coupling between the two constituents. Even for a composite with the mechanical Q of the polymer higher than that of the ceramic, the mechanical Q of the composite is still lower than that of the ceramic except when the ceramic volume content is very low. Hence, in most of piezoceramic polymer composites, the mechanical Q of the ceramic phase plays a major role in determining the quality factor of a 1-3 composite transducer. For the lateral modes in a 1-3 composite, it is found experimentally that the frequencies of the two lowest lateral modes can be determined approximately by the shear wave velocity and the width of the polymer gap over a broad ceramic volume fraction range, suggesting that they correspond to the half-wave standing waves in the polymer gap.
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