Symmetry constraints during the development of anisotropic spinodal patterns

Abstract

Spinodal decomposition is a phase-separation phenomenon occurring at non-equilibrium conditions. In isotropic materials, it is expected to improve the physical properties, in which modulated structures arise from a single system of spinodal waves. However, in anisotropic materials this process is controversial and not very well understood. Here, we report anisotropic spinodal decomposition patterns in single crystals of K-rich feldspar with macroscopic monoclinic 2/m symmetry. The periodicity of the spinodal waves at ~450 nm produces a blue iridescence, typical of the gemstone moonstone. Stripe patterns in the (010) plane, labyrinthine patterns in the (100) plane, and coexistence of the two patterns in the (110) plane are first resolved by scanning Rayleigh scattering microscopy. Two orthogonal systems of spinodal waves with the same periodicity are derived from the features and orientations of the patterns on the crystal surfaces. The orthogonality of the waves is related to the perpendicularity of the binary axis and the mirror plane. Thus, the spinodal patterns must be controlled by symmetry constraints during phase separation at early stages. Unusual and new properties could be developed in other anisotropic materials by thermal treatment inducing two orthogonal systems of periodic spinodal waves.

Structural insights of hierarchically engineered feldspars by confocal Raman microscopy

“…The result of unmixing is a lamellar aggregate formed for lamellas with variable composition. These differences in composition produce changes in the refractive index, which may be used to identify them …”

“…[4,5] Using the elastic scattering of light, areas with slight differences in refractive index or density might be discriminated in a sample, as a source of optical contrast, which allows to obtain more information about the chemical composition. [27][28][29][30][31][32] In this context, the aim of this work is to further characterize the sintered Na rich-based glass-ceramic, paying especially attention to fundamental aspects such as chemical composition and thermal effect in Al-Si ordering of micro and nanocrystals regions. For this purpose, the CRM of sintered feldspars is used to discriminate between phonon response in the micro and nanostructured regions.…”

“…These differences in composition produce changes in the refractive index, which may be used to identify them. [28] Rayleigh light-scattering microscopy is attempted to verify if Raman shift variations observed might be caused by compositional differences or might be corresponded to stresses gradients. Figure 6a illustrates a Rayleigh image taken inside a micrograin that shows a striped pattern with bright and brown zones.…”

“…Additionally, Raman measurements with temperature allow investigating phenomena such as Al, Si‐O tetrahedral distortions due to Al, Si disorder, phase transitions or alkali/alkaline earth site ordering, and local distortion of Si‐Al‐O network . Using the elastic scattering of light, areas with slight differences in refractive index or density might be discriminated in a sample, as a source of optical contrast, which allows to obtain more information about the chemical composition …”

Petrographic Investigation of Target Rock Transformation under High Shock Pressures from the Colônia Impact Crater, Brazil

“…7, No. 1; minerals (Christie, 1968;Ghose et al, 1972;Takeda et al, 1989;Menna et al, 2008;Sánchez-Muñoz et al, 2016). Second, the melting of the quartz + biotite couple generated a complex mixture with a clear fluidal texture of fine aggregates of opaque minerals, globular-looking microcrystalline quartz, and small new grains of biotite.…”