Although neither SrTiO3 nor BaZrO3 has any polar crystalline polymorphs, they may form noncrystalline pyro- and piezoelectric phases [Adv. Mater. 19, 1515 (2007)10.1002/adma.200602149]. These phases and the similar phase of BaTiO3 have been called quasiamorphous. In this Letter, the structure of the quasiamorphous phase of SrTiO3 is examined by the x-ray absorption fine structure technique and found to be built of a random network of polar octahedral TiO6 local bonding units. While in crystalline SrTiO3 all TiO6 octahedra are apex sharing only, in its amorphous and quasiamorphous phases, some octahedra share edges. The polarity of the quasiamorphous phase is due to the partial alignment of the TiO6 octahedra. Such a mechanism is completely different from that of inorganic polar crystals. This mechanism should be possible in a large variety of other compounds that contain similar local bonding units.

The thermal stability of amorphous ionic solids is usually attributed to kinetic considerations related to mass transport. However, there are a number of amorphous ionic solids, which have recently been described, whose unusual resistance to nucleation and subsequent crystallization cannot be explained by mass transport limitations. Examples have been found in a large variety of fields, spanning the range from thin solid films to biomineralization. This poses a question regarding a possible common mechanism for the stabilization of amorphous ionic solids. Here we present a model which explains the formation and thermal stability of quasi-amorphous thin films of BaTiO 3 , one of the amorphous systems recently described which exhibit unusual thermal stability. On the basis of the experimental evidence presented we suggest that nucleation of the crystalline phase can occur only if the amorphous phase undergoes volume expansion upon heating and transforms into an intermediate low density amorphous phase. If volume expansion is unobstructed by external mechanical constraints, nucleation proceeds freely. However, thin films are clamped by a substrate; therefore, volume expansion is restricted and the low-density intermediate phase is not formed. As a result, under certain conditions, nucleation may be completely suppressed and the phase which appears is quasi-amorphous. A quasi-amorphous film is under compressive stress and as long as the mechanical constraints are in place it remains stable at the temperatures that normally lead to crystallization of amorphous BaTiO 3 . Quasiamorphous thin films of BaTiO 3 exhibit pyroelectricity, the origin of which is also explained by the proposed model.

Spontaneous or stress-induced polarization, signifying pyroelectricity and piezoelectricity, respectively, can appear in ionic solids solely due to a non-centrosymmetrical spatial distribution of ions in a polar crystalline structure. Although theory does not impose strict limitations on the size of a polar crystallite, [1,2] the magnitude of pyroelectric and piezoelectric effects of some ceramics, particularly BaTiO 3 , rapidly decrease as grain size diminishes to a few nanometers. [1,3,4] Determination of the minimal number of periodically arranged unit cells for which a crystal retains pyroelectric and piezoelectric properties has become increasingly important due to the rapid incorporation of these materials into nanometer-scale devices. An intriguing complication to this quest arises from the fact that pyro-and piezoelectric effects may exist in structures that lack the spatial periodicity inherent for ionic crystals, but are composed of polar molecules with directional ordering. An example of such a material is a nematic liquid crystal. Spontaneous or stress-induced dipole ordering without fine-tuned positional order is theoretically possible in ionic solids [5] as well; however, only indirect experimental evidence supporting this theory has been presented so far.[6±9] The present work reports on the preparation and pyroelectric properties of quasiamorphous BaTiO 3 thin films that represent a polar ionic solid without spatial periodicity. Pyroelectric amorphous BaTiO 3 films were obtained by passing sputtered amorphous BaTiO 3 films through a steep temperature gradient. As-deposited BaTiO 3 films were stressfree (< ± 30 MPa) with refractive indices in the range of n^= 1.97±2.02, and a very small in-plane±out-of-plane birefringence of n i ± n^= ± (0.002±0.008), confirming film isotropy. A compressive stress of r e = 2.0±2.2 GPa developed in the films passed through the temperature gradient. The refractive index of these films decreased to n^= 1.89/1.94 but the birefringence grew to n i ± n^= 0.03±0.07, corroborating the existence of high in-plane compressive stress.X-ray diffraction (XRD) spectra of the films passed through the temperature gradient were indistinguishable from those of as-deposited films (Fig. 1a). No XRD peaks apart from those of the Si substrate were observed, indicating the absence of a crystalline phase. The volume detection limit of a crystalline phase by XRD calculated from the signal to noise ratio [10] was < 0.3 %. Furthermore, thorough transmission electron microscopy (TEM) investigation only rarely detected the presence of crystalline grains (Fig. 1b) [11] and the concentration of the crystallites estimated from TEM images was far below 0.3 %. In contrast to the similarity with respect to electron and X-ray diffraction analysis, as-deposited films and the films passed through the temperature gradient have distinctly different electrical properties. The films passed through the temperature gradient show a large pyroelectric effect p measured = (1±3) 10 ±9 C cm ±2 K ±1 (5±15 % that of...

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Pyro‐ and piezoelectric quasiamorphous thin films of BaZrO3 and SrTiO3 are reported. This is the first instance of a polar amorphous solid being created from a compound that does not from polar crystalline polymorphs. The pyroelectric and the piezoelectric properties of the quasi‐amorphous SrTiO3 are of the same order of magnitude (10–50 %) as those of the most commonly used crystalline pyro‐ and piezo‐electric materials, such as BaTiO3, Pb(Ti,Zr)O3, and LiNbO3 (see figure).

Cu diffusion in chalcopyrite CuInSe2 was studied directly, using 64Cu as a radioactive tracer. For diffusion from a thin surface layer, the Cu diffusion coefficients at 380 and 430 °C, were found to vary from 10−8 to 10−9 cm2/s. In case of diffusion from a volume source at 400 °C, a value of 10−10 cm2/s was calculated from diffusion profiles. Electromigration of Cu was demonstrated, by applying a strong electric field to a sample and following the redistribution of 64Cu, that had been thermally diffused into the sample, prior to electric field application.

Cesium oxides are materials of great interest to the photodetection industry because of their relatively low work function (∼1 eV). Used mainly as coating films for photoemissive devices, they provide high wavelength thresholds and high photocurrents. However, they are unstable, air-sensitive, and hygroscopic, rendering them short-lived and limiting their applications. Although the technology of these devices is highly developed, their characterization on the micro-and nanoscale suffers from their poor chemical stability and poor crystallinity. In the present study, cesium oxides were synthesized from the elements and were characterized using a combination of chemical and structural analysis techniques. Because the reaction products were extremely sensitive to humidity, sample analysis without atmospheric exposure was essential, and techniques were developed for the transfer of the samples to the measurements systems. Extensive data obtained from X-ray energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and Raman microscopy were obtained. Raman spectra with bands at 103, 742, and 1134 cm -1 strongly confirmed the presence of the oxide, peroxide, and superoxide ions, respectively, as well as the absence of carbonate as an impurity. The A 1g mode of Cs 2 O was detected as an anti-Stokes band at 103 cm -1 . This study provides further insight into the reactivity of the various cesium oxides.

The recent observation of pyroelectricity in quasiamorphous thin films of BaTiO 3 introduced a previously unreported type of polar ionic solid where the appearance of a macroscopic dipole moment is not accompanied by long-range crystal-like order. This poses a question regarding the mechanism of polarity in noncrystalline ionic systems and the nature of their local dipoles. By combining x-ray diffraction and x-ray-absorption fine-structure spectroscopy techniques we have identified the local dipoles as stable but distorted TiO 6 octahedra. The magnitude of the off-center displacement of the Ti ion and the concomitant dipole moment in both quasiamorphous ͑polar͒ and amorphous ͑nonpolar͒ BaTiO 3 were found to be nearly twice as large as those in bulk BaTiO 3. We propose that the mechanism of macroscopic polarity in quasiamorphous BaTiO 3 is in a weak orientational ordering of the TiO 6 bonding units. In this view, one may expect that other amorphous ionic oxides containing stable local bonding units, for example NbO 6 , TiO 6 , or VO 6 , may also form noncrystalline polar phases.