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Multidrug products enable more effective therapies and simpler administration regimens, provided that a stable formulation is prepared, with the desired composition. In this view, solid solutions have the advantage of combining the stability of a single crystalline phase with the potential of stoichiometry variation of a mixture. Here a drug–prodrug solid solution of cortisone and cortisol (hydrocortisone) is described. Despite the structural differences of the two components, the new phase is obtained both from solution and by supercritical CO2 assisted spray drying. In particular, to enter the solid solution, hydrocortisone must violate Etter's rules for hydrogen bonding. As a result, its dissolution rate is almost doubled.

Microhardness of (Cu1–xAgx)7GeSe5I mixed crystals and composites on their base was investigated using the Vickers indenter at room temperature. (Cu1–xAgx)7GeSe5I mixed crystals were obtained using the Bridgman–Stockbarger method. Composites on their base were prepared as a pressed mixture of (Cu1–xAgx)7GeSe5I micropowder and ethylene-vinyl acetate polymer in 90:10 concentration ratio, respectively. Dependences of microhardness versus the indenter penetration depth have been analyzed. Influence of Cu+→Ag+ isovalent cation substitution on the microhardness of (Cu1–xAgx)7GeSe5I mixed crystals and composites on their base have been studied.

The title structures of bis(guanidinium) trioxofluorophosphate, bis(guanidinium) trioxofluorophosphate-phosphite (0.716/0.284), bis(guanidinium) trioxofluorophosphate-phosphite (0.501/0.499), bis(guanidinium) trioxofluorophosphate-phosphite (0.268/0.732), and bis(guanidinium) phosphite are crystal-chemically isotypic. Their structures correspond to the structure of bis(guanidinium) trioxofluorophosphate which was determined by Prescott, Troyanov, Feist & Kemnitz (Z. Anorg. Allg. Chem. 2002, 628, 1749–1755). The P and O atoms of the substituted trioxofluorophosphate and phosphite anions share the same positions while the P-F and P-Hhydrido are almost parallel and oriented in the same direction. Two symmetry-independent anions and two of three symmetry-independent cations are situated on the crystallographic mirror planes. The ions are interconnected by N-H⋯O hydrogen bonds of moderate strength. The most frequent graph set motif is R22(8), which involves interactions between the primary amine groups and the trioxofluorophosphate or phosphite O atoms. Fluorine, as well as the hydrido hydrogen, avoids inclusion into the hydrogen-bond network. The Hirshfeld surface analysis was also performed for the comparison of intermolecular interactions in the title structures of bis(guanidinium trioxofluorophosphate and bis(guanidinium) phosphite. The title crystals were also characterized by vibrational spectroscopy methods (FTIR and Raman) and the second harmonic generation (SHG). The relative SHG efficiency considerably decreases from bis(guanidinium) trioxofluorophosphate to bis(guanidinium) phosphite for the fundamental 1064 nm laser line.

Preparing mixed crystals composed of two or more components is one of the useful approaches to not only modifying the physical properties and chemical reactivity of molecular crystals but also creating their novel functionality. Here we report preparation and photoresponsive properties of two-component mixed crystals containing photochromic bis(benzothienyl)ethene derivatives that show different colors in the closed-ring forms depending on the oxidation state of the benzothiophene groups. The similarity in the molecular structures of the two diarylethenes, which are different from each other only in the oxidation state of the benzothiophene groups, allowed the formation of two-component mixed crystals by recrystallization from mixed solutions containing the two compounds. Irradiating the mixed crystals with light of appropriate wavelengths induced the selective photoisomerizaion of the two diarylethenes, leading to multicolor photochromic performance, such as colorless, orange, yellow, and red. Such molecular crystals with multiresponsive functions can find potential applications in multistate optical recording and multicolor displays. The present results demonstrate that combining differently oxidized diarylethene derivatives is an effective strategy for preparing multicomponent mixed crystals with finely tuned composition and desired photoresponsive properties.

(Cu6PS5I)1–x(Cu7PS6)x and (Cu6PS5Br)1–x(Cu7PS6)x mixed crystals were grown using a direct crystallization technique from the melt. Refractive indices and extinction coefficients for mixed crystals were obtained from the spectral ellipsometry measurements. A nonlinear increase of the refractive indices is revealed with increase of Cu7PS6 content. The dispersion of refractive indices is described in the framework of Wemple–DiDomenico model. The compositional dependences of optical parameters for (Cu6PS5I)1–x(Cu7PS6)x and (Cu6PS5Br)1–x(Cu7PS6)x mixed crystals are analyzed.

(Cu6PS5I)1–x(Cu7PS6)x mixed crystals were grown using the direct crystallization technique from melt (Bridgman–Stockbarger technique). The polymer composites based on (Cu6PS5I)1–x(Cu7PS6)x mixed crystals were prepared. Electrical properties of composites were studied in the frequency range from 10–3 Hz to 2·106 Hz at room temperature. The parallel equivalent circuit with double electric layer assumed at the electrode interface was applied to analyze the frequency dependences of electrical conductivity. It has been shown that the highest value of total electric conductivity is observed for the (Cu6PS5I)0.75(Cu7PS6)0.25-based composite. The further increase of Cu7PS6 content leads to the monotonically decreasing values of total electric conductivity. The ratio of total ionic to electronic components demonstrates the highest value for Cu6PS5I-based composite.

Polymer composites were prepared from (Ag 1–x Cu x ) 7 GeS 5 I mixed crystals grown using Bridgman–Stockbarger method. The impedance measurements were performed at room temperature in the frequency range 10 –3 –2·10 6 Hz. The frequency dependences of electrical conductivity and dielectric permittivity for composites based on (Ag 1–x Cu x ) 7 GeS 5 I mixed crystals were obtained. The Nyquist plots for (Ag 1–x Cu x ) 7 GeS 5 I-based composite has been analyzed. The influence of cation Ag→Cu substitution on electrical conductivity of composites based on (Ag 1–x Cu x ) 7 GeS 5 I mixed crystals has been studied.

Abstract This study focused on how the local structures in pure [N(CH3)4]2ZnBr4 crystal are affected by the partial replacement of Zn2+ ions with Cu2+ ions. The structures and phase transition temperatures TC of perovskite-type [N(CH3)4]2Zn1-x Cu x Br4 (x = 0, 0.5, 0.7, and 1) mixed crystals were almost unchanged by the partial doping of Cu2+ ions. The environments for the local structures of [N(CH3)4]2Zn1-x Cu x Br4 mixed systems were studied according to differences in the chemical shifts of the 1H magic angle spinning (MAS) NMR, 13C cross-polarization (CP)/MAS NMR, and 14N NMR spectra. The 1H and 13C NMR results showed that the local environments of 1H and 13C nuclei near TC are not affected by substituting Zn2+ ions with Cu2+ ions, whereas the 14N NMR results showed that the local environment is affected near TC. Consequently, the main indicators of the phase transition in [N(CH3)4]2Zn1-x Cu x Br4 are related to the ferroelastic characteristics with different orientations.

K2NiXCo(1−X) (SO4)2·6H2O (KCNSH) mixed crystal is a promising material for solar blind optical filters, combining high transparency in the ultraviolet range with effective suppression of the visible spectral region. Increasing the mechanical strength of these crystals is important to enable them to be machined in the manufacture of optical elements. A comprehensive study of the inhomogeneities and crack resistance of KCNSH crystal as a function of the growth conditions was carried out. The influence of the radial and mosaic inhomogeneity, as well as other structural defects, on the crack resistance of the crystals was analyzed. To assess the crack resistance of crystals, the parameters ca (crack length), c/a (the ratio of crack length to the size of the indentation), and KC (fracture toughness) were used. The correctness of the obtained results was analyzed. The conditions for growing KCNSH crystals with the best crack resistance were determined on the basis of the results of the study. It is shown that growing the mixed crystals using the temperature difference technique with a peripheral solution supply into the shaper provides the best crystal quality.

The mosaic and radial inhomogeneity of shaped mixed crystals of K2NixCo(1–x)(SO4)2·6H2O (KCNSH) were studied depending on the supercooling of solution, its velocity and its method of supply into the shaper. It was shown that mosaic inhomogeneity could be suppressed when solution is supercooled to about 2 °C. Peripheral supply of the solution (tangential to the wall of the shaper to create a “swirling” flow) with a rate of 55–135 cm/s provides better composition uniformity along the crystal surface in comparison with upright supply of the solution (flow is perpendicular to the crystal surface).

Mixed (Cu6PS5I)1–x(Cu7PS6)x crystals were grown using a direct crystallization technique. Being based on the X-ray diffraction data, their crystal structure was studied, showing face-centred cubic lattice for Cu6PS5I-rich solid solutions (х < 0.12) and primitive cubic lattice for Cu7PS6-rich (0.84 < x < 1) solid solutions. These structural data correlate with the Raman spectra where, besides the common features typical for the argyrodite-type Cu6PS5I and Cu7PS6 crystals, weaker bands characteristic only for the end-point compounds are revealed in the corresponding compositional intervals.

Impedance Spectroscopy was performed to examine the electrical conductivity on KH2PO4 KDP, (NH4)H2PO4 ADP and K1-x(NH4)xH2PO4 (x = 0.076, 0.118, 0.357, 0.857, 0.942) crystals with increasing temperature. They were grown by solvent evaporation method. Zview simulation software was used to theoretically fit electrical conductivity results as a function of frequency (1-106 Hz) and temperature (20-160 ºC) with equivalent circuits. These dielectric-type materials become ionic conductors upon heating. Proton jumps in hydrogen bonds, heavier ions migration (K+ and NH4+), and rotation and reorientation of ammonium groups contributed to electrical conduction. This conduction behavior follows the Arrhenius equation with which the activation energies were determined at different temperature ranges. For ADP-rich (x > 0.8) and pure ADP crystals the conductivities are higher than those for KDP-rich (x < 0.2) and pure KDP. Lattice defects may reduce electrical conductivities in the crystals with intermediate x composition. Complex permittivity ac and complex conductivity ac were also obtained for these crystals.

The change in the surface morphology of the (001) and (110) faces of K2CoxNi(1−x)(SO4)2·6H2O (KCNSH) mixed crystal, depending on the supercooling solution, has been studied under various conditions by laser interferometry. The experiments were carried out in both static mode, by changing the solution composition, and in dynamic mode, by changing the flow velocity. The conditions for the onset and suppression of the reaction of the isomorphic replacement leading to the formation of mosaic micro-inhomogeneity in mixed crystals have been studied. The mechanism of the reaction of isomorphic replacement has been analyzed depending on the shift of the solution composition from the initial one. For the first time, it has been observed that the reaction of isomorphic replacement may occur through a layer-by-layer mechanism.

This review, for the first time, summarizes the results of studies of the defect formation mechanisms in mixed crystals grown from aqueous solutions. The general mechanism of interaction of a crystal with a foreign solution is described (reaction of isomorphous replacement). As a result of this reaction, the crystal surface turns into a mosaic of local areas where multidirectional processes (dissolution and growth) occur simultaneously. Data on mosaic microinhomogeneity, which is a new type of composition inhomogeneity inherent solely to multicomponent crystals, is presented. A new mechanism for the mismatch stress relaxation in heterocompositions of brittle crystals grown from low-temperature solutions is described; in this case, the formation of misfit dislocations is impossible and stress relaxation occurs due to the formation of numerous inclusions at the interface. The general concept of growing high-quality mixed crystals from solutions is described, using the example of K2(Co, Ni)(SO)2 · 6H2O (KCNSH) mixed crystals.