Yingxiang Li

Interface characterization of SrTiO3/Sr/Si heterostructure through X-ray reflectivity

The growth of hetero-epitaxial strontium titanate (SrTiO3) on single-crystal silicon (Si) substrate is of considerable scientific interest because of its wide range application. Unlike other hetero-epitaxial systems, there exists a fairly large lattice mismatch between SrTiO3 and Si. This leads to the possibility of strain in SrTiO3 thin film. In order to prevent the formation of amorphous SiO2 phase and interdiffusion of component atoms at the interface, an ultrathin strontium (Sr) layer is deposited on the underlying Si-substrate. The X-ray diffraction (XRD) is used for characterization of hetero-structures. In this paper, we report the characterization of SrTiO3 thin film on Si (100) substrate with Sr interlayer by a variety of X-ray measurements. Based on the data obtained from SrTiO3 thin film, the growth characteristics of the sample is objectively appreciated. The sample is prepared by laser molecular beam epitaxy (L-MBE) under optimized conditions of substrate temperature and oxygen pressure. 2?/? scan indicates a high crystallization quality and epitaxial grown of SrTiO3 thin film in the nanometre scale. ?-scans have further revealed the in-plane orientation relationship between SrTiO3 and Si. The ?- and c- lattice parameters of the SrTiO3 thin film are found to be 0.3898, and 0.3901 nm, respectively, which suggests a slight elastic distortion. More detailed investigations by X-ray reflectivity have therefore been carried out, in order to get better understanding to the effect of the buried heterointerface.

Determining the Quality Factor of Dielectric Ceramic Mixtures with Dielectric Constants in the Microwave Frequency Range

Microwave dielectric ceramic materials are extensively utilized in microwave applications because of their high dielectric constants and quality factors. These applications also require ceramics of zero temperature coefficients at the resonant frequency (τf), which can be realized through mixing a ceramic that one is interested in with another ceramic with −τf, or by performing the ionic substitution. With the mixing/ionic substitution, it is indispensable to compute the quality factors precisely. Previous study indicates that the quality factor depends on the grain size, porosity, internal strain, structure, phase evolution, and conductivity etc. Here we derive a quality factor formula based on the definition, which works very well for multiphase composites, single phase solid solutions, and equivalent ionic substituted single phase materials. Our formula calculation and fits to the previous experimental results demonstrate that the quality factor of the ceramic mixtures strongly depend on the dielectric constants and the dielectric constant variation index. Our results suggest that the impacts from grain size, porosity, and internal strain etc. can be summarized to the dielectric constant or dielectric constant variation index, which is of great importance for future design of high performance microwave dielectric ceramics.

The optimization of microwave dielectric properties of the Li 2 ZnTi 3 O 8 ceramic by the phase purity control

In recent reports, the microwave dielectric properties of Li2ZnTi3O8 ceramic deviate largely from the optimal value. In this paper by the Rietveld refinement method, the co-existence of the secondary phases is confirmed which is due to the zinc volatilization. Thus, the excessive ZnO addition is introduced to obtain a high purity Li2ZnTi3O8 phase. Microwave dielectric properties are theoretically calculated to prove the above statement, based on the property indices of these phases. The calculated result is consistent to the measured data, with relative deviation around 5%. The optimized properties make the ceramic a promising ceramic candidate for the microwave applications.