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The chemical strain effect describes a mechanism of stress relaxation in solids that can be attributed to the conversion of elastic energy into chemical energy of point defects. Experimental confirmation of this effect is presented here for the case of thin self‐supported films of the ionic conductor Ce0.8Gd0.2O1.9. If heated slowly, (< 5 °C min–1) these films remain flat within the temperature range of 25–180 °C. If heated more rapidly than ∼ 20 °C min–1, the films buckle above 53 °C, but after ∼ 3–30 min at elevated temperatures, they become flat again, demonstrating that stress‐relaxation has taken place. The degree of stress reduction observed is consistent with the value calculated for this system using Boltzmann statistics in the case of small strain. These findings confirm the concept of stress adaptability in solids that we introduced in Part I and suggest that a large class of such materials, which exhibit the chemical strain effect, is likely to be found.

A model of structural transformations of amorphous into quasi‐amorphous BaTiO3is suggested. The model is based on previously published data and on X‐ray photoelectron spectroscopy data presented in the current report. Both amorphous and quasi‐amorphous phases of BaTiO3are made up of a network of slightly distorted TiO6octahedra connected in three different ways: by apices (akin to perovskite), edges, and faces. Ba ions in these phases are located in the voids between the octahedra, which is a nonperovskite environment. These data also suggest that Ba ions compensate electrical‐charge imbalance incurred by randomly connected octahedra and, thereby, stabilize the TiO6network. Upon heating, the edge‐to‐edge and face‐to‐face connections between TiO6octahedra are severed and then reconnected via apices. Severing the connections between TiO6octahedra requires a volume increase, suppression of which keeps some of the edge‐to‐edge and face‐to‐face connections intact. Transformation of the amorphous thin films into the quasi‐amorphous phase occurs during pulling through a steep temperature gradient. During this process, the volume increase is inhomogeneous and causes both highly anisotropic strain and a strain gradient. The strain gradient favors breaking those connections, which aligns the distorted TiO6octahedra along the direction of the gradient. As a result, the structure becomes not only anisotropic and non‐centrosymmetric, but also acquires macroscopic polarization. Other compounds may also form a quasi‐amorphous phase, providing that they satisfy the set of conditions derived from the suggested model.

The elastic behavior of solids with a large concentration of interacting point defects has been analyzed. The analysis predicts that, in such solids, mechanical stress may be partially relieved by a shift in the association/dissociation equilibrium of the point defects. Association/dissociation of the point defects in response to an external stress will proceed until the decrease in elastic energy is balanced by the increased chemical energy of the defect distribution. The resulting change in the linear dimensions may be called “chemical strain”, in analogy to the previously studied “chemical stress”. A solid in which chemical strain may develop in response to external stress should exhibit two distinct Young's moduli: relaxed, on a time scale which allows the defects to reach equilibrium; and unrelaxed, on a time scale which is too short for the defect equilibrium to be established. Our analysis suggests that materials exhibiting the chemical‐strain effect are capable of reversible adaptation to external mechanical constraints. Measurements on a self‐supported film of Ce0.8Gd0.2O1.9strongly support the theoretical predictions.

The lattice parameter of nanocrystalline ceria films prepared by sputtering was monitored as a function of annealing temperature. Within the temperature range of 150–420 °C, an equilibrium with atmospheric oxygen is established within a few hours, whereas grain growth does not occur. On the basis of the experimental results and analysis of literature data, we present a model that posits the formation of a non-uniform grain structure with stoichiometric interiors and oxygen deficient boundaries. This model, based on defect thermodynamics, correctly describes the dependence of the lattice parameter of nanocrystalline ceria on annealing temperature and grain size and can be extended to other materials as well.

We investigated mechanical stress in thin freestanding BaTiO3films prepared on bare silicon and on silicon, covered by a 120 nm thick, randomly oriented Al2O3buffer. Films prepared on bare silicon by RF sputtering are essentially stress‐free. However, they disintegrate after substrate removal. In contrast, the films prepared on the Al2O3buffer have high tensile stress, but retain their structural integrity after separation from the substrate. Substrate removal is accompanied by film corrugation; at the same time, the freestanding films resonate mechanically. This seeming contradiction can be understood on the basis of a recently developed theory of 2D clamping in thin ferroelectric films.

We show how phase separation, in the form of a redistribution of impurities (dopants in a semiconductor), can occur at impurity concentrations that are more than one order of magnitude lower than hitherto observed. This phenomenon results from the balance between long-range electrostatic repulsion and the elastic attraction of the dopants, which deforms the anisotropic host lattice. We observed such a phase separation for Ag in (Cd, Hg)Te at Ag concentrations < 0.02 at. %. This also leads to the formation of a thermodynamically (as opposed to kinetically) stable p-njunction in the 2-phase region. Searching for phase separation at such low concentrations requires highly sensitive analyses, here made possible because of the difference in conductivity type between the phases.

The compound Bi1/2Ag1/2TiO3 has been synthesized, for the first time, at 14−14.5 GPa and 1000 °C using the uniaxial split sphere anvil type press (USSA-2000). The structure of the quenched powder sample was refined from synchrotron X-ray diffraction data using the Rietveld method. At room temperature, Bi1/2Ag1/2TiO3 exhibits an orthorhombic distortion of the cubic perovskite structure and was assigned to a space group of Ibam and lattice parameters of a = 5.48970(4) Å, b = 5.51954(5) Å, and c = 7.77585(7) Å. The refinements are consistent with a random distribution of Bi³⁺ and Ag⁺ on the A-sites. Diffraction results at various temperatures show two phase transitions as the temperature is increased. At 573 K, tetragonal symmetry is observed and was assigned to a space group of I4/mcm with lattice parameters of a = 5.51664(8) Å and c = 7.8134(2) Å, while at 673 K, the cubic perovskite structure, with space group Pm&thremacr;m and a = 3.90607(8) Å, was determined. Plane capacitor dielectric contact measurements at 100 kHz gave a dielectric constant of 354 at ambient temperature for the sample. The dielectric constant increases with temperature and reaches a local maximum of 834 at 578 K. After heating the sample to 778 K and cooling back to room-temperature, both dielectric and diffraction measurements provide evidence for a small but irreversible change in the stoichiometry.

Here we present the results of the study of electromechanical performance of the Ce0.8Gd0.2O1.95 (CGO) self-supported thin circular membranes with aluminum and titanium as contact electrode materials. The electromechanical performance of both membranes was investigated using highly sensitive interferometric technique and showed two principal excitations mechanisms: common electrostriction and thermal contribution due to the Joule heating. Operating the membranes at frequencies about MHz results in significant contribution of the thermal excitation due to a large power dissipation for every electrode. The excitation of the membrane with aluminum electrodes at the frequencies about 1 Hz leads to the formation of the Schottky barrier at the interface with CGO. That is why the electromechanical response was almost independent on frequency and electric field. Membrane with titanium electrodes showed a prevalence of electrostriction effect with weak frequency dispersion and significant enhancement of the response with temperature.

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