Isothermal crystallization of isotactic polypropylene at high pressures (from 200 to 250 MPa) have been carried out using a high-pressure dilatometer leading to a pure γ-form, as revealed by WAXD. The melting temperatures at the same pressures have been determined to assess the pressure effect on the equilibrium melting temperature by the Hoffman-Weeks analysis. The crystallization times have been analyzed according to the Hoffman-Lauritzen theory and corrections introduced to take into account the pressure effects on both the equilibrium melting temperature and the diffusion process. This analysis showed a transition from crystallization regime II to regime III for an undercooling of 53.7 K. The lateral and fold surface free energies were evaluated. Furthermore, the morphology of the samples investigated by polarized light microscopy, density measurements, and SAXS depends only on the crystallization undercooling, as a result of the influence of pressure on the equilibrium melting temperature. Moreover, the lamellar thickness experimental data agree well with the theoretical calculation.

No abstract

No abstract

No abstract

No abstract

This paper deals with the temperature dependence of electrical and physical features of various kinds of solidly mounted resonators (SMR). The presented bulk acoustic wave (BAW) devices are designed for the 2 GHz application. The temperature coefficient of frequency (TCF) is determined from measurements well above the temperature range defined for wireless telecommunication system specifications. Therefore, evolution of electromechanical coupling factors and quality factors at resonance and antiresonance are also monitored. Results of characterizations show the trend for a subsequent theoretical temperature compensation study by using analytical modeling. To improve accuracy of modeling, an attempt to extract temperature dependence of dielectric permittivity epsilon(33) and piezoelectric coefficient e(33) is made. Finally, a well-known analytical model is modified to take into account the temperature dependence of length, density, stiffness coefficient, dielectric permittivity, and piezoelectric coefficient. Modeling highlights the need to deposit a material with positive temperature coefficient of stiffness on the top electrode. Realistic thickness of such a layer is determined. At the same time, it is necessary to adjust piezoelectric and electrode thin film thicknesses for simultaneously keeping a constant antiresonance frequency, reaching a zero temperature coefficient of frequency for antiresonance, and minimizing the decrease in the coupling factor because of the mass-loading deposition.

No abstract

No abstract