Fengxia Yang

Improved two-temperature model and its application in femtosecond laser ablation of metal target

An improved two-temperature model to describe femtosecond laser ablation of metal target was presented. The temperature-dependent heat capacity and thermal conductivity of the electron, as well as electron temperature-dependent absorption coefficient and absorptivity are all considered in this two-temperature model. The tailored two-temperature model is solved using a finite difference method for copper target. The time-dependence of lattice and electron temperature of the surface for different laser fluence are performed, respectively. The temperature distribution of the electron and lattice along with space and time for a certain laser fluence is also presented. Moreover, the variation of ablation rate per pulse with laser fluence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the temperature dependence of heat capacity, thermal conductivity, absorption coefficient and absorptivity in femtosecond laser ablation of metal target must not be neglected. The present model will be helpful for the further experimental investigation of application of the femtosecond laser.

A new comprehensive model for the pyroelectric property of 0-3 ferroelectric composites

A new comprehensive model has been developed for the pyroelectric activity of 0-3 ferroelectric composites which includes additional contributions from the electrical conductivity of the constituents and the frequency of measurement when the secondary pyroelectric effect resulting from the coupled thermoelectroelastic behaviour is considered. The boundary conditions are obtained in terms of the Laplace equation and Maxwells equations. The analytical expressions have been derived for primary and secondary pyroelectric coefficients. The effects of the electrical conductivity of the matrix σm and the measuring frequency f on the pyroelectric property have been investigated in detail. Possible methods for improving the pyroelectric effect are also discussed. Our model can reflect comprehensively the pyroelectric property of the material and shows reasonably good agreement with experimental data.

Effect of electrical conductivity on the polarization behaviour and pyroelectric, piezoelectric property prediction of 0–3 ferroelectric composites

We have investigated the effect of electrical conductivity of the constituents on the poling behaviour of the ceramic inclusions in 0–3 ferroelectric composites which comprise a dilute suspension of spherical particles uniformly distributed in the matrix material. A new model for the pyroelectric and piezoelectric properties in terms of the poling conditions (poling field and poling time) has been developed to include electrical conductivity. Simulated results show that conductivity plays an important role in the poling process. Properly increasing the conductivity of the matrix σm can enhance the polarization in the ceramic inclusion of the composite Pi, thereby making the poling of the composite more efficient. In contrast, higher conductivity of the ceramic inclusion σi results in lower polarization Pi, which is unfavourable to the poling of the composite. These results provide insights into the observed behaviour of 0–3 composites. The model predicts the pyroelectric and piezoelectric properties under different poling conditions, which agree well with the corresponding experimental data.

Model for the magnetoresistance of the silver-rich Ag2+δSe and Ag2+δTe thin films

This work proposes a model for linear magnetoresistance (MR) by considering Ag2+δSe and Ag2+δ Te thin films as two-dimensional two-component (silver metal component and semiconductor component) compositions. The model addresses the dependence of the MR on the magnetic field, temperature and the conductivities of the two components without the magnetic field. The model predictions agree well with the available experimental data. It is found that there is a critical volume fraction of the silver component at which the MR reaches a maximum value. We interpret the occurrence of the critical volume fraction as a consequence of the percolation between silver particles and the variation of the disorder of the microstructure in the material.

A three-dimensional resistor network model for the linear magnetoresistance of Ag2+δSe and Ag2+δTe bulks

A network model for the linear magnetoresistance (MR) of the Ag2+δSe and Ag2+δTe bulks is proposed. The bulk sample is considered as a two-phase (the metal phase and the semiconductor phase) composite and dispersed into a three-dimensional resistor network. The network is constructed from six-terminal resistor units and the mobility of carriers within the network has a modified Gaussian distribution, i.e., a Gaussian distribution with two constraint conditions. The modified Gaussian distribution is related with the mobility of carriers in the two phases and the volume fraction of the metal phase. The model predicts that the MR increases linearly with the increasing magnetic fields and does not show the saturation at high field. Moreover, the temperature dependence of the MR predicted by the model is discussed. A good agreement is found between the theoretical MR predictions and the available experimental data.

The coupled thermoelectroelastic behaviors of biphasic piezocomposites

A theoretical framework for effective thermoelectroelastic moduli is developed in terms of the Dunn-Taya theory and Dunn’s model. This theoretical framework provides a physical insight and reflects directly the contribution of each phase and the influence of interaction (or the coupling effect) between phases. The coupled thermoelectroelastic behaviors are discussed.