We construct a Landau–Ginzburg thermodynamic potential, and the corresponding phase diagram for pristine and slightly doped bismuth ferrite, a ferroelectric antiferromagnet at room temperature. The potential is developed based on new X-ray and neutron diffraction experiments complementing available data. We demonstrate that a strong biquadratic antiferrodistortive-type coupling is the key to a quantitative description of Bi1−x La x FeO3 multiferroic phase diagram including the temperature stability of the antiferromagnetic, ferroelectric, and antiferrodistortive phases, as well as for the prediction of novel intermediate structural phases. Furthermore, we show that “rotomagnetic” antiferrodistortive–antiferromagnetic coupling is very important to describe the ferroelectric polarization and antiferrodistortive tilt behavior in the R3c phase of BiFeO3. The Landau–Ginzburg thermodynamic potential is able to describe the sequence of serial and trigger-type phase transitions, the temperature-dependent behavior of the order parameters, and the corresponding susceptibilities to external stimuli. It can also be employed to predict the corresponding ferroelectric and antiferrodistortive properties of Bi1−x La x FeO3 thin films and nanoparticles by incorporating the gradient and surface energy terms that are strongly dependent on the shape, size, and preparation method.

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In this study we report on the dielectric, ferroelectric, and piezoelectric properties of the conventional polyvinylidene fluoride/trifluoroethylene, P(VDF‐TrFE), copolymer of composition 70/30 mol.% with fillers on the basis of lead zirconate titanate (PZT). (Pb0.75Ba0.24Sr0.01)(Zr0.53Ti0.47)O3 (BPZT) fillers with concentrations from 10 to 50 vol.% are additional components in the P(VDF‐TrFE) piezoelectric polymer. Dielectric spectroscopy and the characterization of ferroelectricity and piezoelectricity in the P(VDF‐TrFE)/BPZT composites are performed over a wide temperature range from 150 to 420 K. The dependence of the effective dielectric permittivity for the composites under investigation on the filler concentration is analyzed by the Lichtenecker mixing rule. The approximation model of effective medium is also applied to explain the impact of BPZT fillers on the ferroelectric and piezoelectric properties of P(VDF‐TrFE)/BPZT composites.

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Germanium (Ge) nanowires were fabricated by electrochemical deposition on titanium‐coated silicon substrate. Arrays of nanowires with different mean diameters were obtained using indium nanoparticles of various sizes as centers of nucleation. Raman spectroscopy was used to establish the structural properties of nanowires under different laser excitation intensities. Cycles of measurements with different intensities demonstrated irreversible changes in the structure. Initial study with minimal excitation intensity of 3 W/cm2 displayed that the spectra are descriptive of amorphous Ge. Further study at increased intensities led to the transformation of Raman spectra to the shapes that can be attributed to crystalline Ge. Detailed analysis of spectra shapes for samples with different mean diameters of Ge nanowires after exposure to high intensity laser radiation allows to estimate the fraction of the crystalline phase in Ge nanowires. The spectra of a sample irradiated by He–Ne laser were compared with thermally annealed sample in a vacuum at 150 °C. A similar shape of the obtained spectra indicates on the thermal nature of the effect, which leads to a change in the observed structural properties. This change under even slight heating can be explained by thermal isolation of nanowires from the substrate.