Characterizations Of Residual Stress And Texture In Thin Film And Properties Of Oriented Ferroelectric Film

Residual stress inevitably exists in the thin film with substrate, due to the structural and thermal misfit of the thin film/substrate system. In addition, because crystal is usually anisotropic and polycrystalline film generally suffers various anisotropic external field (such as electromagnetic field, temperature field, stress field, and so on) in the course of preparation, polycrystalline film usually exhibit the feature of texture. It is well accepted that texture and residual stress in polycrystalline film have significant effects on film properties.Although there are several common methods to characterize texture, such as pole figure, inverse pole figure, orientation distribution function (ODF) and preferred orientation parameter methods, only ODF method can quantitatively and qualitatively characterize the texture existed in materials. Obviously, it is extravagant to obtain ODF or pole figure for the characterization of fiber texture, usually existing in films and extruded metals, because the case of fiber texture is markedly simpler than that of rolled texture. In this paper, the description of fiber texture was simplified at primarily, and then the physical meaning ofω-scan was discussed in detail. Subsequently, a new qualitative and quantitative method for fiber texture was proposed. The proposed methods can be used in any crystal system. For experimental verification, both the proposed method and ODF method were performed on one sputtered Pt film. Comparing with the results from the proposed method and ODF method, it is clear that the proposed method is valid in characterization of fiber texture.For the evaluation of the residual stress in sample, a grain-interaction model should be employed. On the basis of the proposed ideal of local grain-interaction model, two local grain-interaction models (local Voigt and local Reuss models) were proposed. For the proposed local models, only the mechanical conditions of the grains contributing to diffraction experiment are constrained by assumptions. Evidently, the constraints from the proposed local models are looser than that from traditional models, thus the proposed local models are more compatible with physical reality than the traditional models. As experimental verification for the proposed grain-interaction models, X-ray diffraction measurements were performed on a sputtered platinum film. To avoid the fortuitous result, several reflections were considered in analysis of macroscopic residual stress. The researched results for the Pt film showed that the consistent residual-stress results for the two local models and several reflections were obtained. This case indicates that both the two local models can be employed to validly determine macroscopic residual stress.For specifically understanding the effects of fiber texture and residual stress on the physical properties of ferroelectric perovskite thin films, as examples, the 2-2-type BaTiO3/CoFe2O4 multiferroic composite film and PbTiO3 film were theoretically discussed on the bases of Landau-devonshire theory, the simplified description of fiber texture and the assumptions of the interaction among electric domains. The formulas to respectively describe the effect of fiber texture and residual stress on the magnetoelectric effect of composite film and the transition behavior of ferroelectric perovskite film were established. Finally, the effects of fiber texture and residual stress were in detail discussed by numerical simulations.If the phase transition of grains in ferroelectric thin film does not occur at the same temperature, there may exist several phases in the ferroelectric thin film, and some physical properties of the ferroelectric thin film would be abnormal. The PZT 52/48 thin films with (100)-oriented texture were studied, and the results of XRDθ-2θscan show that Cm and T phases exist in the PZT films. The above result proves that the assumption of diffuse phase transition is appropriate. Subsequently, the reason of diffuse phase transition in the PZT films were analyzed on the principle of mechanical equilibrium condition, and the analyzed results prove that the phase transition mechanism of locally disordered displacements is valid. Furthermore, the ferroelectric and pyroelectric properties of the PZT films with different thickness were studied, respectively. The researched results indicated that the preferred orientation and the content of Cm phase severely affect ferroelectric and pyroelectric properties of the PZT films. Moreover, the diffuse phase transition from Cm phase to T phase occurred with increasing temperature, and induced an abnormal tendency of pyroelectric coefficient against temperature. It is very important that the diffuse phase transition can validly enhance the pyroelectric coefficient of PZT film. This case has important significance in practical application.