We present a comparative study between the structural, electronic and ferroelectric properties of pristine ZnO, Zn93.75Sr6.25O and Zn93.75Ba6.25O using first-principle calculations and the modern ...theory of polarization. In the comparison, the Sr-O and Ba-O bonds turn out to be larger than those of the undoped ZnO structure. This produces an increase in the volume of the supercell and a slight decrease in polarization of ZnO. Moreover, the directional nature of the shared charge distribution between the O and Zn ions confirms the presence of covalence in the Zn-O bonds and the maximum polarization was observed in pristine ZnO. The results reported in this study have led to an identification of key factors that govern the ferroelectric properties of doped ZnO.
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Much work has been done already on pure and doped BiFeO3 (BFO), however, renewed interest has emerged when considered as a viable photovoltaic material. It has been shown that, for this purpose, ...spontaneous polarization and energy gap are relevant physical quantities. In this theoretical-experimental work, we have studied the possibility of enhancing the spontaneous polarization and reducing the BFO bandgap by replacing 10% of the site A ions of the perovskite structure with La. The structural, electronic and optical properties of (Bi0.9La0.1)FeO3 were investigated using pristine BFO as a reference. A rhombohedral crystal structure was determined after La substitution and its corresponding bandgap of 2.49 eV was smaller than that of pure BFO. Theoretically, the spontaneous polarization (Ps) of the BFO increased with the incorporation of La up to a value of 103 C cm−2, showing its effect on the ferroelectric properties. Moreover, the theoretical results and experimental measurements of the optical properties demonstrated the reduction of the optical gap.
This theoretical work presents magnetic, electronic and optical properties of SrFe12-xAlxO19 (x = 0.5; 1; 1.5) solid solutions using first-principles calculations based on density functional theory. ...A decrease in the magnetic properties of SrFe12O19 is predicted when doped with the Al ions. It was found that the Al ions preferentially replace Fe ions at 2a and 12k sites. On the other hand, SrFe11.5Al0.5O19 and SrFe11Al1O19 solid solutions behave like a semiconductor, while SrFe10.5Al1.5O19 solid solution showed a metallic response. From the optical analysis, incorporating the Al ions can benefit the polarizability of the medium. For the SrFe11.5Al0.5O19 (Al2a) and SrFe11Al1O19 (Al2a-2a) solid solutions, the incorporation of Aluminum ions results in the reduction of the gap, making it a more useful material for catalytic applications.
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•Hypothetical SrFe12-xAlxO19 (x = 0.5; 1; 1.5) solid solutions.•A decrease in the magnetic properties of SrFe12O19 when doped with the Al ions.•Al ions preferentially replace Fe ions at 2a and 12k sites in ground states.•SrFe12-xAlxO19 (x = 0.5; 1) present a semiconductor behavior; SrFe10.5Al1.5O19 showed metallic response.•SrFe12-xAlxO19 solid solutions can be prefigured for catalytic applications.
This work demonstrates that the rf-sputtering technique, combined with appropriate heat treatments, is potentially effective to develop new materials and devices based on oxide-interface and strain ...engineering. We report a study of the structural-physical properties relationship of high crystalline quality, highly oriented and epitaxial thin films of the lead-free (K0.5Na0.5)0.985La0.005NbO3 (KNNLa) compound which were successfully deposited on Nb-doped SrTiO3 substrates, with orientations 100 (NSTO100) and 110 (NSTO110). The crystalline growth and the local ferroelectric and piezoelectric properties were evaluated by piezoresponse force microscopy combined with transmission electron microscopy and texture analysis by X-ray diffraction. Conditioned by the STO surface parameters, in the KNNLa films on NSTO100 coexist a commensurate 001-tetragonal phase and two incommensurate 010-monoclinic phases; while on NSTO110 the KNNLa films grew only in an incommensurate 101-monoclinic phase. Both samples show excellent out-of-plane polarization switching patterns consistent with 180° domains walls; while for KNNLa/NSTO100 ferroelectric domains grow with the polarization pointing down, for KNNLa/NSTO110 they prefer to grow with the polarization pointing up. Comparing with previous reports on epitaxial KNN films, we find our samples to be of very high quality regarding their crystalline growth with highly ordered ferroelectric domains arrangements and, consequently, great potential for domain engineering.
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