A new atomic layer deposition (ALD) process for nanocrystalline tin dioxide films is developed and applied for the coating of nanostructured materials. This approach, which is adapted from non‐hydrolytic sol‐gel chemistry, permits the deposition of SnO2 at temperatures as low as 75 °C. It allows the coating of the inner and outer surface of multiwalled carbon nanotubes with a highly conformal film of controllable thickness. The ALD‐coated tubes are investigated as active components in gas‐sensor devices. Due to the formation of a p‐n heterojunction between the highly conductive support and the SnO2 thin film an enhancement of the gas sensing response is observed.

The concentration range of the stability of polar (R3c) and antipolar phases in the Bi 1Àx RE x FeO 3 (RE-La -Dy) solid solutions has been determined by X-ray study of the polycrystalline samples. Both polar and antipolar phases become less stable with a decrease of the rare earth ionic radii. It is stimulated by a reduction of the rare-earth ions polarizability with a decrease in ionic radii. The antipolar phase is characterized by a weak ferromagnetic state, whereas the polar one exhibits dominantly antiferromagnetic behavior near the polar-antipolar morphotropic boundary. The local piezoelectric response decreases with increase in antipolar phase content in the mixed polarantipolar structural state. It is suggested that the piezoelectric activity is associated with polar (R3c) phase.

The LaCo1−xFexO3 compounds have been investigated by means of neutron powder diffraction (NPD), x-ray powder diffraction (XPD) and magnetization measurements. The NPD and XPD patterns were successfully refined as rhombohedral (x≤0.5) and orthorhombic (x≥0.6). The temperature-induced transition from the rhombohedral phase into the orthorhombic one is characterized by a two-phase crystal structure state. Magnetization and neutron powder measurements have revealed that compounds with x<0.4 exhibit a paramagnetic-like behaviour, whereas for x≥0.4 samples a weak ferromagnetic component was observed. The NPD patterns were successfully refined by admitting a Gz spatial orientation of the antiferromagnetic vector. The magnetic properties of the LaCo1−xFexO3 samples can be explained assuming a low spin state of the Co3+ ions, whereas antiferromagnetism is caused by magnetic interactions between the Fe3+ ions. Based on the obtained data the combined crystal and magnetic phase diagram has been constructed.

Crystal structures of Bi1–x Lnx FeO3 systems (Ln = La, Nd, Eu) are studied using X‐ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1–x Lax FeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Pnma at x > 0.5. The mixed‐phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1–x Ndx FeO3 system. In the case of Bi1–x Eux FeO3 series the unit cell is rhombohedral (R3c) at x < 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Pnma and Imma phases that do not allow conventional ferroelectricity. The ferroelectric R3c phase exhibits metamagnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln3+ leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of crystal structure, ferroelectric, and magnetic properties of polycrystalline Bi1−xDyxFeO3 (0.1≤x≤0.2) samples was carried out. X-ray diffraction study revealed composition-driven rhombohedral-to-orthorhombic R3c→Pnma phase transition at x∼0.15. Both structural phases were found to coexist in a broad concentration range. Piezoresponse force microscopy found suppression of the parent ferroelectric phase upon dysprosium substitution. Magnetometric study confirmed that the A-site doping induces appearance of a weak ferromagnetic behavior. Both the ferroelectric and magnetic properties were shown to correlate with a structural evolution.

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Recent observations of unusual ferroelectricity in thin films of HfO 2 and related materials have attracted broad interest to the materials and led to the emergence of a number of competing models for observed behaviors. Here we develop the electrochemical mechanism of observed ferroelectric-like behaviors, namely the collective phenomena of elastic and electric dipoles originated from oxygen vacancies formation in the vicinity of film surfaces, as well as from grain boundaries and other types of inhomogeneities inside the film. The ferroelectric phase is induced by the "electrochemical" coupling, that is the joint action of the omnipresent electrostriction and "chemical" pressure, which lead to the sign change of the positive coefficient α in the quadratic term αP 2 in the order-disorder type thermodynamic functional depending on polarization P. Negative coefficient α becomes the driving force of the transition to the long-range ordered ferroelectric phase with the spontaneous polarization P in the direction normal to the film surface. Using the above ideas, we estimated that the reversible ferroelectric polarization, as high as (0.05 -0.2) C/m 2 , can be induced by oxygen vacancies in HfO 2 films of thickness less than (20 -30) nm. Semi-quantitative agreement with available experimental data is demonstrated.