Internal stress in doped NH4Cl:Mn2+ crystals

Anomalous Isomorphism and Mixed Crystals in the Systems NH4Cl:(Cu,Mn)

“…Our goal here is to address all these issues and to track the evolution of crystal organization, kinetics, micromorphology, crystal optics, and imperfections as a function of impurity concentration. Some of these issues have already been covered in our earlier publications. − Here, we summarize all these findings and add new data on phase identification, epitaxial relationships, and anomalous birefringence.…”

“…According to Xray data, impurities aggregate as oriented individual crystallites in the bulk of ammonium chloride single crystal. 22,26 Formation of such a crystal requires strong lateral interaction between adsorbed molecules that can be described in the simplest way using the Fowler−Guggenheim adsorption isotherm: 34…”

“…This agrees with the idea that formation of mixed crystals requires matching of crystal lattices in all three dimensions. 36,38 X-ray fluorescence and X-ray diffraction mapping 26 show changes in the overall Me concentration and fractions of guest phases over the crystal face. This emphasizes mass transfer inhomogeneity in the diffusion boundary layer and its consequences: competition between different guest phases and enrichment of the face centers in phases with higher copper content.…”

“…This assumption is wrong. According to X-ray data, impurities aggregate as oriented individual crystallites in the bulk of ammonium chloride single crystal. , Formation of such a crystal requires strong lateral interaction between adsorbed molecules that can be described in the simplest way using the Fowler–Guggenheim adsorption isotherm: C = false[ k 2 normalF θ / ( 1 − θ ) false] exp false[ prefix− k 1 normalF θ / R T false] where the first parameter, k 2F , characterizes adsorbate–adsorbent interactions and corresponds to k L in the Langmuir isotherm; R is the universal gas constant, and T is the absolute temperature. The second parameter k 1F characterizes intermolecular adsorbate–adsorbate interactions.…”

“…ε j = Δ d j || / a NH 4 Cl corresponds to mismatch between host and guest phases in the growth plane (Table ), and a NH 4 Cl is the lattice constant of ammonium chloride. The birefringence was calculated as Δ n = | n 0 3 (π 12 – π 11 )( c 11 – c 12 )ε/2|, where π ij are piezooptic constants (π 11 – π 12 = 3.3 × 10 –12 , ), c ij are elastic stiffness constants ( c 11 – c 12 = 29.5 GPa), and n 0 = 1.639 is the refractive index of NH 4 Cl. In this geometry, the optical indicatrix is uniaxial with the optic axis parallel to the (100) face normal.…”