A nonlinear thermodynamic formalism is developed to calculate the pyroeletric property of epitaxial single domain SrTiO_(3)/Si heterojunctions by taking into account the thermal expansion misfit strain at diferent temperatures.It has been demonstrated that the crucial role was played by the contribution associated with the structure order parameter arising from the rotations of oxygen octahedral on pyroelectricity.A dramatic decrease in the pyroelectric cofficient due to the strong coupling between the polarization and the structure order parameter is found at ferroelectric T_(p1)-T_(p2) phase transition.At the same time,the thermal expansion mismatch between film and substrate is also found to provide an additional weak decrease of pyroelectricity.The analytic relationship of the out-of-plane pyroeletric coefficient and dielectric constant of ferroeletric phases by considering the thermal expansion of thin films and substrates has been determined for the first time.Our research provides another avenue for the investigation of the pyroelectric effects of ferroic thin films,especially,such as antiferroelectric and muliferroic materials having two or more order parameters.
Gang BaiDongmei WuQiyun XieYanyan GuoWei LiLicheng DengZhiguo Liu
The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO_2 have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO_2. Compared with the energy band structure of pure CeO_2, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO_2 were explained through the absorption spectra and the selection rule of the band-to-band transitions.
