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Laser-fabrication of complex, highly oriented three-dimensional ferroelectric single crystal architecture with straight lines and bends is demonstrated in lanthanum borogermanate model glass using a high repetition rate femtosecond laser. Scanning micro-Raman microscopy shows that the c-axis of the ferroelectric crystal is aligned with the writing direction even after bending. A gradual rather than an abrupt transition is observed for the changing lattice orientation through bends up to approximately 14 degrees. Thus the single crystal character of the line is preserved along the bend through lattice straining rather than formation of a grain boundary.

Single-crystal architectures in glass, formed by a solid-solid transformation via laser heating, are novel solids with a rotating lattice. To understand the process of lattice formation that proceeds via crystal growth, we have observed in situ Sb2S3 crystal formation under X-ray irradiation with simultaneous Laue micro X-ray diffraction (μXRD) pattern collection. By translating the sample with respect to the beam, we form rotating lattice single (RLS) crystal lines with a consistently linear relationship between the rotation angle and distance from nucleation site. The lines begin with a seed crystal, followed by a transition region comprising of sub-grain or very similarly oriented grains, followed by the presence of a rotating lattice single crystal of unrestricted length. The results demonstrate that the primary cause of lattice rotation within RLS crystals is the densification accompanying the glass → crystal transformation, rather than stresses produced from the difference in thermal expansion coefficient of the two phases or paraelectric → ferroelectric transition during cooling to ambient temperature.

We have investigated the occurrence of the sometimes observed grain boundaries, as initial seed is extended to form line in laser-fabricated single-crystal architecture in glass (SCAG). In particular, for Sb2S3 SCAG in Sb-S-I glass as a model system, grain boundaries are formed during the transition from laser-written initial seed dot to crystal line. Such grain boundaries during the growth of Sb2S3 crystals occur in 16SbI3–84Sb2S3 glass, whereas they are absent in Sb2S3 glass. We correlate this difference in tendency to form multiple grains with the relative glass forming ability i.e. the dynamics of nucleation and crystal growth as determined by differential scanning calorimetry (DSC). On the basis of this understanding, methods to minimize the appearance of grain boundaries in the transition region are suggested.

Atomic arrangements systemically deviating from the classic definition of single crystal lattice have been known in spherulites for over a century. However, their unusual curved lattice could not be exploited for useful applications due to their uncontrolled orientations and lattice curvatures. Heating of glass with focused laser, electron, or X‐ray beam has yielded well‐defined conditions for forming single crystal architectures. Furthermore, by controlling the conditions of irradiation and confinement by glass matrix for a given system, desired lattice curvature (rotations and twists) can be reproducibly introduced into these crystals. Here, we review several examples of laser‐fabricated crystals with curved lattices in glass using a common coordinate system, which helps to establish correlations between processing parameters and lattice curvature. The mechanisms of lattice deformations are discussed along with potential methods to control the orientation of the initially formed seeds that determine the lattice orientations of the end product. The recent developments of laser‐fabrication of single crystal architectures in glass with controlled heating profile appear promising for engineering the curvature of their lattices. [ABSTRACT FROM AUTHOR]

Congruent crystallization of antimony sulphoiodide ( SbSI) glass of stoichiometric composition, which is prepared successfully for the first time using rapid melt-quenching, has been investigated using differential scanning calorimetry ( DSC). The results for glass powder show a glass transition at 127°C and two separate exothermal peaks with maxima around 140°C and 190°C. The ratio of the intensities of the exothermal peak at ~190°C to the peak at ~140°C increases as the particle size and heating rate are increased, but their total enthalpy remains constant at 62 ± 2 J/g for all DSC runs. Surface heating of the glass induced by a 520 nm CW laser shows two contracted regions: needle-like crystalline formations at low temperature and bulk crystallization at high temperature. The observed phenomena and DSC results suggest two different kinds of crystallization of the SbSI phase: one-dimensional crystallization at low temperature which starts from the sample surface and three-dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The origin of the two different crystallizations can be traced to the strong anisotropy of the SbSI crystal structure due to the weak van der Waals interaction between covalent-ionic chains (Sb2S2I2) n. [ABSTRACT FROM AUTHOR]

We demonstrate that suitable thermal treatment of biocompatible CaO–Na2O–P2O5–SiO2 glasses prepared by the usual melt-quench results in spinodal phase separation and crystallization of phases at very different length scales. Selective chemical leaching of these phases allows the formation of interconnected multi-modal porosity, with pore size ranging from several nanometers to tens of micrometers. Such novel nano–macroporous glasses have potential applications as superior bioscaffolds. [ABSTRACT FROM AUTHOR]

Laser heating can be used to produce single crystal architectures in glass with a lattice that rotates at a constant rate. Such metamaterials can offer properties that are disallowed by conventional crystal structures. To establish the mechanism of this lattice rotation, we used transmission electron microscopy (TEM) to directly observe and characterize dislocations in Sb 2 S 3 crystal lines fabricated in Sb-S-I glass as a model system. The lattice rotation calculated from the density and Burgers vectors of edge dislocations agrees with lattice rotation values experimentally determined by electron backscatter diffraction (EBSD) and selected area diffraction patterns (SADP). These results provide the first direct proof of the dislocation mechanism of lattice rotation in rotating lattice single (RLS) crystals, and very likely other forms of growth actuated bending, twisting and noncrystallographic branching as seen in spherulites. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A carefully controlled femtosecond laser irradiation offers the possibility of fabricating high quality, 3D functional single-crystal patterns designed for integrated optical devices deep inside glass. Notwithstanding, a general theory relating particular irradiation conditions to crystal growth dynamics and resulting morphologies remains to be established. To overcome this challenge, crystal lines written in glass under varying conditions are investigated in this work by optical microscopy, scanning electron microscopy, and electron backscatter diffraction in the congruently crystallizing LaBGeO 5 model system. We show that despite a strongly preferential orientation of the optic axis along the direction of laser scanning, typical morphologies of fs laser-written crystals in this system are inhomogeneous due to low-angle grain boundaries and rotations or inversions of the preferential axis. Nevertheless, uniform single crystals can be produced under optimized irradiation conditions. The theoretical dynamics of crystal growth is developed within the unique environment of a moving laser-induced melt to explain these results, including the role of competitive growth in establishing the preferential lattice orientation; the effects of temperature gradient and focal scan rate in establishing crystal morphology and cross-section shape; and most notably, the specific design criteria that must be met for stable single-crystal growth. [ABSTRACT FROM AUTHOR]

EXAFS analysis is performed on equiatomic GeSe and GeTe films to elucidate changes in the local atomic environments induced by crystallization. It reveals for both the films that the 4:2 configuration dominates in their as-deposited amorphous state. In their crystallized state, however, the 3:3 configuration prevails together with quasi-crystalline Ge clusters. The two chalcogenide films exhibit very similar characteristics such as hidden glass transition phenomenon during heating, dominance of the 3:3 configuration in their melt state, decreased optical bandgap upon crystallization, and reduced temperature dependence of electrical conduction accompanied with crystallization. These common properties are partly attributed to the structural changes identified through our EXAFS analysis. In particular, their previously reported non-ohmic current-voltage behaviors associated with the phase switching and the threshold switching are explained in terms of the local structural information. The special phase-change properties of the equiatomic GeSe film is explicated by its amorphous structure. [ABSTRACT FROM AUTHOR]

Abstract: The role of structure in the crystallization of Ge x Te100− x model system suitable for phase-change applications is established by determining the local environment of each constituent using EXAFS analysis. Across the compositional spectrum, both constituents satisfy the (8-N) rule in the amorphous state except that the Ge atoms are surrounded by ∼3.4 neighbors in the stoichiometric composition. The estimation of homopolar Ge–Ge and Te–Te bonds indicates that chemical order is preserved less for Ge than for Te atoms. The crystallized stoichiometric film consists of Ge clusters in addition to GeTe crystals, implying that the latter has appreciable concentration of Ge vacancies. [Copyright &y& Elsevier]