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To obtain materials with desired properties, material compositions are primarily altered, whereas thin films offer additional unique avenues. By combining state‐of‐the‐art first‐principles calculations and experimental investigations of thin films of strontium titanate as an exemplary representative of a broad class of perovskite oxides and the extensive family of ferroelectrics, a novel approach is presented to achieving superior material responses to external stimuli. The findings reveal that substrate‐imposed deformations, or strains, significantly alter the frequencies and magnitudes of atomic vibrations in thin films. Consequently, material‐specific response‐stimulus coefficients can become strain‐dependent. The strain‐dependent Curie constant, which characterizes the dielectric response to thermal stimuli, is theoretically justified and experimentally validated. Given that atomic vibrations fundamentally govern various response coefficients in a wide range of materials, and that thin films are typically deformed by substrates, it is anticipated that unprecedented responses can be generally attained through substrate‐induced control of atomic vibrations in thin films. Many material‐specific coefficients, which relate external stimuli and functional responses, are constants governed by atomic vibrations. This work demonstrates the concept of controlling such response coefficients by deformations, or strain, through strain‐induced changes in atomic vibrations. As a proof of concept, the dependence of the Curie constant on substrate‐imposed strain in SrTiO3 films is theoretically predicted and experimentally validated.

Optical index of refraction n is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO 3 with thickness ∼10 nm grown on different single-crystal substrates. The index n in the transparency spectral range (n ≈ 2.1 - 2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index n in air exceeds that in an oxygen ambience by δn ≈ 0.05 - 0.2. The thermo-optical behaviour n(T) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO 3 .

The deposition of multilayer coating of NiTi is carried out by a thermal plasma spraying process on a stainless steel substrate. The deposition of melted NiTi particles creates an adhesion layer on the substrate with the subsequent formation of multilayer coating with a certain thickness. Six layers of coating are created to achieve a certain thickness in terms of the sprayed sample. This paper aims to investigate multilayer NiTi coatings created through a thermal plasma process. The key variable feed rate was considered, as well as its effect on the microstructure characteristics. The shape memory effect associated with the coating properties was analyzed in detail. The variable feed rate was considered one of the most important parameters in the thermal plasma spraying process due to its ability to control the quality and compactness of the coating structure. The coatings were characterized by examining their microstructure, thermal, chemical, and microhardness. The indent marks were made/realized along the cross-section surface for the analysis of crack propagation resistance and wear properties. The coating’s surface did not display segmentation crack lines. Nevertheless, the cross-sectional surfaces showed evidence of crack lines. There were eutectic zones of the interlamellar structure observed in the structure of the coating. The plasma-sprayed samples from thermo-mechanical analysis of the hysteresis curve provide strong confirmation of the shape memory effect.

The quality of NiTi coating influences the thermal, microstructural, and mechanical behavior of the material produced by plasma spraying. To understand the behavior of the coating, the study has been designed and planned at two different plasma powers with various feed rates. NiTi as shape memory layers emerge as promising protective coatings on the surface of substrates against corrosion or wear. In the present investigation, NiTi multilayers were produced by thermal plasma spraying using NiTi (50 at. %) powder as the feedstock material. This work illustrates the studies of the microstructure, porosity of the coating layers, phase detection, hardness values, shape memory behavior, and the formation of samples produced by different spraying parameters. The porosity within coating layers has been analyzed based on the various shape factors of pores that correlate with the hardness and mechanical behavior of the samples. This work will explore the quality of the coating in terms of its porosity and compactness, which will affect the performance of the shape memory behavior. The functional coating of NiTi will have a significant influence on the durability of the material’s performance against corrosion.

MnO thin films with various thicknesses and strains were grown on MgO substrates by pulsed laser deposition, then characterized using x-ray diffraction and infrared reflectance spectroscopy. Films grown on (001)-oriented MgO substrates exhibit homogenous biaxial compressive strain which increases as the film thickness is reduced. For that reason, the frequency of doubly-degenerate phonon increases with the strain, and splits below Néel temperature TN due to the magnetic-exchange interaction. Films grown on (110)-oriented MgO substrates exhibit a huge phonon splitting already at room temperature due to the anisotropic in-plane compressive strain. Below TN, additional phonon is activated in the IR spectra; this trend is evidence for a spin-order-induced structural phase transition from tetragonal to monoclinic phase. Total phonon splitting is 55 cm-1 in (110)-oriented MnO film, which is more than twice the value in bulk MnO. This result is evidence that the nearest neighbor exchange interaction, which is responsible for the magnetically driven phonon splitting, is greatly increased in compressively strained films.

Optical index of refraction is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO with thickness ∼10 nm grown on different single-crystal substrates. The index in the transparency spectral range (  ≈ 2.1 - 2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index in air exceeds that in an oxygen ambience by  ≈ 0.05 - 0.2. The thermo-optical behaviour ( ) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO .

Optical index of refraction n is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO sub(3) with thickness ~10 nm grown on different single-crystal substrates. The index n in the transparency spectral range (n [approximate] 2.1-2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index n in air exceeds that in an oxygen ambience by delta n [approximate] 0.05-0.2. The thermo-optical behaviour n(T) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO sub(3).

In search for the origins of the extraordinary low twinning stress of Ni-Mn-Ga magnetic shape memory alloys we studied the thermally induced changes of structure in Ni\\(_{50}\\)Mn\\(_{25+x}\\)Ga\\(_{25-x}\\) (\\(x\\)=2.7--3.9) single crystal samples and compared them with twinning stress dependences. The alloys exhibited transformation to five-layered (10M) martensite structure between 297 to 328 K. All samples exhibited magnetic shape memory effect. Just below the transformation temperature the samples had very low twinning stress of about 0.1--0.3 MPa, which increased with decreasing temperature. The structural changes were monitored using X-ray diffraction in the temperature range 173--343 K. The 10M structure was approximated by monoclinic lattice with the unit cell derived from the cubic unit cell of the parent L2\\(_{1}\\) phase. With decreasing temperature, the lattice parameters \\(a\\) and \\(\\gamma\\) increased, \\(c\\) decreased, while \\(b\\) was nearly constant. For \\(x\\leq3.5\\), sudden sharp changes in \\(a\\) and \\(b\\) parameters additionally occurred, resulting in \\(a=b\\) in some regions of the phase diagram, which might be related to the refinement of twin structure of 10M martensite on nanoscale. The temperature dependences of lattice parameter \\(\\gamma\\) (and \\(c\\) or \\(c/a\\)) correlate well with the temperature dependences of twinning stress in agreement with the prediction by a microstructural model of twin boundary motion. On the contrary, there is no correlation between \\((a-b)\\) and twinning stress. This indicates no significant role of \\(a/b\\) twins or laminate in twin boundary motion mechanism and low twinning stress.