Polymorphic Transition Research Articles

Polymorphic phase transitions in triglycerides and their mixtures studied by SAXS/WAXS techniques: In bulk and in emulsions

Triacylglycerols (TAGs) exhibit a monotropic polymorphism, forming three main polymorphic forms upon crystallization: α, β’ and β. The distinct physicochemical properties of these polymorphs, such as melting temperature, subcell lattice structure, mass density, etc., significantly impact the appearance, texture, and long-term stability of a wide range products in the food and cosmetics industries. Additionally, TAGs are also of special interest in the field of controlled drug delivery and sustained release in pharmaceuticals, being a key material in the preparation of solid lipid nanoparticles. The present article outlines our current understanding of TAG phase behavior in both bulk and emulsified systems. While our primary focus are investigations involving monoacid TAGs and their mixtures, we also include illustrative examples with natural TAG oils, highlighting the knowledge transfer from simple to intricate systems. Special attention is given to recent discoveries via X-ray scattering techniques. The main factors influencing TAG polymorphism are discussed, revealing that a higher occurrence of structural defects in the TAG structure always accelerates the rate of the α → β polymorphic transformation. Diverse approaches can be employed based on the specific system: incorporating foreign molecules or solid particles into bulk TAGs, reducing drop size in dispersed systems, or using surfactants that remain fluid during TAG particle crystallization, ensuring the necessary molecular mobility for the polymorphic transformation. Furthermore, we showcase the role of TAG polymorphism on a recently discovered phenomenon: the creation of nanoparticles as small as 20 nm from initial coarse emulsions without any mechanical energy input. This analysis underscores how the broader understanding of the TAG polymorphism can be effectively applied to comprehend and control previously unexplored processes of notable practical importance.

Observation of a temperature dependent anomaly in the UV translucency of milk useful for UV-C preservation techniques

Milk fat globules and casein micelles are the dispersed particles of milk that are responsible for its typical white turbid appearance and usually make it difficult to treat with modern ultraviolet light (UV) preservation techniques. The translucency of milk depends largely on the refractive indices of the dispersed particles, which are directly affected by temperature changes, as incorporated triglycerides can crystallize, melt or transition into other polymorphs. These structural changes have a significant effect on the scattering properties and thus on the UV light propagation in milk, especially by milk fat globules. In this study, a temporary minimum in the optical density of milk was observed within UV wavelength at 14 °C when heating the milk from 6 to 40 °C. This anomaly is consistent with structural changes detected by a distinct endothermic peak at 14 °C using differential scanning calorimetry. Apparently, the optical density anomaly between 10 and 20 °C disappears when the polymorphic transition already has proceeded through previous isothermal equilibration. Thus, melting of equilibrated triglycerides may not affect the RI of milk fat globules at ca. 14 °C as much as melt-mediated polymorphic transitioning. An increased efficiency of UV-C preservation (254 nm) at the translucency optimum was demonstrated by temperature-dependent microbial inactivation experiments.

Системи CeO2—Ln2O3 (Ln = лантаноїди ітрієвої підгрупи, Y2O3

Based on the analysis of literature data from the experimentally constructed phase diagrams of CeO2—Ln2O3 systems (Ln = Tb—Lu), as well as the temperatures of polymorphic transformations of oxides of rare earth elements (REEs), approximate phase diagrams of the indicated system were constructed in the entire range of temperatures and concentrations. Cerium dioxide crystallizes in the cubic type of fluorite crystal lattice and has no polymorphic transformations in the entire temperature range until melting at 2400 ºC. The solubility based on CeO2 is higher than based on other lanthanide oxides. The components of the systems show complete solubility below solidus with the formation of solid solutions with a structure of the fluorite-type F. The appearance below the solidus regions of solid solutions based on polymorphic modifications of lanthanide oxides H, A, B and C with different width leads to the formation of cascades of peritectoid transformations. During the transition in the Tb—Lu series, their temperatures gradually increase, which is associated with an increase in the temperatures of polymorphic transformations of Tb—Lu oxides. Hypothetical phase diagrams of the CeO2—Ln2O3 series (Ln = Tb—Lu, Y) with adjustments according to such regularities of interaction during the transition from Tb to Lu. Experimental verification of the phase diagrams structure of the considered systems is possible when conducting experiments using increased pressures of oxygen-containing media, or by thermodynamic calculations. Keywords: REE oxides, Y2O3, CeO2, polymorphic transformation of REE, phase diagrams.

Similarity between Shock-Induced Polymorphic Transitions in the Silica System

Similarity between Shock-Induced Polymorphic Transitions in the Silica System

The use of polymorphic state modifiers in solid lipid microparticles: The role of structural modifications on drug release performance

This study investigates the correlation between the structural and release properties of solid lipid microparticles (MPs) of tristearin containing 5 % w/w of four different liquid additives used as crystal modifiers: isopropyl myristate (IM), ethyl oleate (EO), oleic acid (OA) and medium chain triglycerides (MCT). All additives accelerated the conversion of the unstable α-form of tristearin, formed after the MPs manufacturing, to the stable β-polymorph and the transformation was completed within 24 h (for IM and EO) or 48 h (for OA and MCT). The kinetic of polymorphic transition at 25 °C was investigated by simultaneous synchrotron SAXS/WAXS and DSC analysis after melting and subsequent cooling of the lipid mixture. After crystallization in the α-phase, additives accelerate the solid-solid phase transformation to β-tristearin. SAXS data showed that two types of structural modifications occurred on MPs during storage: compaction of the crystal packing (slight decrease in lamellar thickness) and crystal growth (increased number of stacked lipid lamellae). The release behavior of a model hydrophilic drug (caffeine) at two different amounts (15 % and 30 %) from MPs was studied in water and biorelevant media simulated the gastric and intestinal environment. It was particularly significant that the introduction of IM, EO and MCT were able to prolong the drug release in water, passing from a diffusion-based Higuchi kinetics to a perfect zero-order kinetic. Moreover, the overall release profiles were higher in biorelevant media, where erosion/digestion of MPs was observed. After 6 months, a moderate but statistically significant change in release profile was observed for the MPs with IM and EO, which can be correlated with the time-dependent structural alterations (i.e. larger average crystallite size) of these formulations; while MPs with OA or MCT displayed stable release profiles. These findings help to understand the correlation between release behavior, polymorphism and supramolecular‐level structural modification of lipid formulations containing crystal modifiers.

Thermal and structural behavior of mango (Mangifera indica L) kernel fat from three Ivorian varieties

AbstractMango (Mangifera indica L.) seeds is an interesting source of fat, rich in stearic (St) and oleic (O) acid with three major triacylglycerols (TAG): StOSt, StOO, and StLSt. The kernel fat content and quality depend however on the varieties and their origin. The objective of this study was to investigate the crystallization and polymorphic behavior of mango kernel fat extracted from three selected Ivorian varieties which differ in terms of TAG composition: Kent (KT), Djakoumankoun (DN) and Brooks (BR). The isothermal crystallization behavior was examined at 15 and 20°C by pulsed nuclear magnetic resonance, differential scanning calorimetry, x‐ray diffraction (XRD) and polarized light microscope. Under static conditions, DN crystallized faster, followed by BR, then KT. At 15°C, an unusual evolution was observed for both DN and BR, which can be explained by a melt‐mediated polymorphic transition from α into more stable forms. Using a differential scanning calorimetry (DSC) stop‐and‐return technique, different crystallization behaviors were also observed. Isothermal XRD experiments confirmed that the kinetics of the polymorphic transformation was different within the three samples, even if the three fats were β‐3L‐tending. At 15°C, KT transformed from liquid state to stable form without passing through α‐form, while DN and BR crystallized first into α‐from which transformed further to β′, then into stable β‐form. At 20°C, DN and BR crystallized directly from liquid to β′, which later transformed into β‐form while KT did not crystallize under the same conditions. The huge differences observed result from the differences in the TAG profiles, mainly in the StOO and StOSt content.

THERMODYNAMIC PROPERTIES OF SOME TERNARY COMPOUNDS OF THE ARGYRODITE FAMILY

Compounds of the argyrodite family are valuable environmentally friendly functional materials with mixed ion-electronic conductivity, thermoelectric, photovoltaic, optical, and other properties. This paper presents the results of a thermodynamic study of the Cu8GeS6 and Cu8GeSe6 compounds - representatives of this family using the EMF method with Cu4RbCl3I2 solid electrolyte in the 295-430 K temperature range. From the EMF measurement data, the partial molar functions of copper were calculated in both crystal modifications of the Cu8GeS6 and Cu8GeSe6 compounds, undergoing polymorphic transformations at 330 and 335 K, respectively. Based on solid-phase equilibria diagrams of the Cu-Ge-S(Se) systems, the potential-forming reactions responsible for the partial molar functions of copper in the alloys were determined and the thermodynamic functions of formation and standard entropies of both modifications of these compounds, as well as the thermodynamic functions of their polymorphic transitions, were calculated. The work also presents and analyzes the thermodynamic data for compounds of the argyrodite family available in the literature

Thermochemistry, Structure, and Optical Properties of a New β-La2(SO4)3 Polymorphic Modification

A new polymorphic modification of lanthanum sulfate was obtained by thermal dehydration of the respective nonahydrate. According to powder X-ray diffraction, it was established that β-La2(SO4)3 crystallized in the C2/c space group of the monoclinic system with the KTh2(PO4)3 structure type (a = 17.6923(9), b = 6.9102(4), c = 8.3990(5) Å, β = 100.321(3)°, and V = 1010.22(9) Å3). Temperature dependency studies of the unit cell parameters indicated almost zero expansion along the a direction in the temperature range of 300–450 K. Presumably, this occurred due to stretching of the [LaO9]n chains along the c direction, which occurred without a significant alteration in the layer thickness over the a direction. A systematic study of the formation and destruction processes of the lanthanum sulfates under heating was carried out. In particular, the decisive impact of the chemical composition and formation energy of compounds on the thermodynamic and kinetic parameters of the processes was established. DFT calculations showed β-La2(SO4)3 to be a dielectric material with a bandgap of more than 6.4 eV. The processing of β-La2(SO4)3 with the Kubelka–Munk function exhibited low values below 6.4 eV, which indicated a fundamental absorption edge above this energy that was consistent with LDA calculations. The Raman and infrared measurements of β-La2(SO4)3 were in accordance with the calculated spectra, indicating that the obtained crystal parameters represented a reliable structure.

Amorphization of different furosemide polymorphic forms during ball milling: Tracking solid-to-solid phase transformations

Ball milling is used, not only to reduce the particle size of pharmaceutical powders, but also to induce changes in the physical properties of drugs. In this work we prepared three crystal forms of furosemide (forms Ⅰ, Ⅱ, and Ⅲ) and studied their solid phase transformations during ball milling. Powder X-ray diffraction and modulated differential scanning calorimetry were used to characterize the samples after each milling time on their path to amorphization. Our results show that forms Ⅰ and III directly converted into an amorphous phase, while form Ⅱ first undergoes a polymorphic transition to form Ⅰ, and then gradually loses its crystallinity, finally reaching full amorphousness. During ball milling of forms Ⅰ and Ⅱ, the glass transition temperature (Tg) of the amorphous fraction of the milled material remains almost unchanged at 75 °C and 74 °C, respectively (whilst the amorphous content increases). In contrast, the Tg values of the amorphous fraction of milled form III increase with increasing milling times, from 63 °C to 71 °C, indicating an unexpected phenomenon of amorphous-to-amorphous transformation. The amorphous fraction of milled forms I and II samples presented a longer structural relaxation (i.e., lower molecular mobility) than the amorphous fraction of milled form III samples. Moreover, the structural relaxation time remained the same for the increasing amorphous fraction during milling of forms I and II. In contrast, the structural relaxation times were always shorter for the amorphous fraction of form III, but increased with increasing amorphous content during milling, confirming amorphous-to-amorphous transformation.

A high-pressure single-crystal X-ray diffraction study of potassium guaninate hydrate, K+·C5H4N5O-·H2O.

The crystal structure of potassium guaninate hydrate, K+·C5H4N5O-·H2O, was studied in the pressure range of 1 atm to 7.3 GPa by single-crystal diffraction using synchrotron radiation and a laboratory X-ray diffraction source. Structural strain was compared to that of the same salt hydrate on cooling, and in 2Na+·C5H3N5O2-·7H2O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at ∼4-5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to ∼1.4 GPa.

Di-Alkyl Adipates as New Phase Change Material for Low Temperature Energy Storage

This work is a contribution to the thermal characterization of a selected binary system of two di-n-alkyl adipates that can be used as phase change material for thermal energy storage at low temperatures. The construction of the solid–liquid phase diagram using differential scanning calorimetry (DSC), complemented with Raman Spectroscopy studies for the system composed by diethyl and dibutyl adipates is presented. The solidus and liquidus equilibrium temperatures were determined by DSC for the pure components and 30 binary mixtures at selected molar compositions were used to construct the corresponding solid–liquid phase diagram. The binary system of diethyl and dibutyl adipates presents eutectic behaviour at low temperatures. The eutectic temperature was found at 240.46 K, and the eutectic composition was determined to occur at the molar fraction xdibutyl = 0.46. Additionally, the system shows a polymorphic transition, characteristic of dibutyl adipate, occurring at ca. 238 K, confirmed by optical microscopy. To the best of our knowledge, no reference to the phase diagram of the present system could be found in the literature. Raman spectroscopy was essential to complement the construction of the phase equilibrium diagram, enabling the identification of the solid and liquid phases of the system. Finally, the liquidus curve of the phase diagram was also successfully predicted using a suitable fitting equation, being the root mean square deviation of the data from the correlation equal to 0.54 K. In addition, this fitting operation enabled a correct prediction of the eutectic composition of the system.

Xiongnu ancient nomad inlaid buckles (2nd-1st centuries BC): Multi-analytical research

The recently excavated burial grounds of Ala-Tey of the 2nd-1st centuries BCE, located in the basin of the Ulug-Khem (Yenisei) River, at the entrance to the Sayan Canyon of the Yenisei, belong to the archaeological monuments on the territory of the Republic of Tuva (Central Asia) and are associated with the Xiongnu culture. The part of preserved inlays and the base of buckles were investigated using Raman and FTIR spectroscopy. By Raman spectroscopy in the buckle base, amorphous carbon was identified. The investigation also revealed the mineral contribution in the FTIR spectra of buckles plates such as kaolinite (Al2O3·2SiO2·2H2O) and quartz (SiO2) in addition to the absorbance bands of some organic components. Buckles inlays mineral composition was identified via Raman spectroscopy. Two different types of blue-green minerals were found: turquoise (CuAl6(PO4)4(OH)8·4H2O) and muscovite (KAl2(Si3Al)O10(OH)2). According to the Raman spectroscopy data all red inlays contain α-quartz and inclusions of hematite. The red inlay transparency is associated with the presence of moganite (polymorphic monoclinic modification of SiO2). The white inlay material consists of aragonite (CaCO3). The results of the study are relevant for better understanding of Xiongnu belt buckles materials and choosing appropriate strategies of its conservation.

Enhanced electrocaloric effect in KNN-based ceramic via polymorphic phase transition

A large adiabatic temperature change (ΔT) in lead-free ceramics is highly desired to develop eco-friendly and high efficiency solid-state refrigeration device based on electrocaloric effect (ECE). However, a large ΔT is often obtained near high Curie temperature (Tc > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K0.48Na0.535)0.03Li0.07(Nb0.99Sb0.01)O3-xBaZrO3 (x = 0, 0.02, 0.04 and 0.06) ceramics were synthesized through a conventional solid-state sintering method. A polymorphic phase transition (PPT) region is constructed by composition engineering to achieve large ECE near the ambient temperature. A ΔT of 0.48 K under 50 kV/cm is obtained at 60 °C by using the direct measurement in KNLNS-0.02BZ ceramic with coexistence of R-O-T phase. This work suggests that building multi-phase coexistence is a feasible design scheme in order to achieve ECE near the room temperature.

Optimizing Output Power Density in Lead-Free Energy-Harvesting Piezoceramics with an Entropy-Increasing Polymorphic Phase Transition Structure.

It is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs) to address the energy dilemma and meet environmental protection requirements. However, the low output power densities limit further promotion of lead-free PEHs for use in daily life. Here, an entropy-increasing strategy is proposed to achieve an increased output power density of 819 μW/cm3 in lead-free potassium sodium niobate (KNN)-based piezoceramics by increasing the configuration entropy and realizing nearly two times the growth compared with low-entropy counterparts. Evolution of the energy-harvesting performance with increasing configuration entropy is demonstrated systematically, and the excellent energy-harvesting properties achieved are attributed to the enhanced lattice distortion, the flexible polarization configuration, and the high-density randomly distributed nanodomains with the entropy-increasing effect. Moreover, excellent vibration fatigue resistance and variable temperature output power characteristics were also realized in the PEH prepared by the proposed entropy-increasing material. The significant enhancement of the comprehensive energy-harvesting performance demonstrates that the construction of KNN-based ceramics with high configuration entropy represents an effective and convenient strategy to enable design of high-performance piezoceramics and thus promotes the development of advanced PEHs.

Crystal Structures and Phase Stability of the Li2S-P2S5 System from First Principles.

The Li2S-P2S5 pseudo-binary system has been a valuable source of promising superionic conductors, with α-Li3PS4, β-Li3PS4, HT-Li7PS6, and Li7P3S11 having excellent room-temperature Li-ion conductivity >0.1 mS/cm. The metastability of these phases at ambient temperature motivates a study to quantify their thermodynamic accessibility. Through calculating the electronic, configurational, and vibrational sources of free energy from first principles, a phase diagram of the crystalline Li2S-P2S5 space is constructed. New ground-state orderings are proposed for α-Li3PS4, HT-Li7PS6, LT-Li7PS6, and Li7P3S11. Well-established phase stability trends from experiments are recovered, such as polymorphic phase transitions in Li7PS6 and Li3PS4, and the instability of Li7P3S11 at high temperature. At ambient temperature, it is predicted that all superionic conductors in this space are indeed metastable but thermodynamically accessible. Vibrational and configurational sources of entropy are shown to be essential toward describing the stability of superionic conductors. New details of the Li sublattices are revealed and are found to be crucial toward accurately predicting configurational entropy. All superionic conductors contain significant configurational entropy, which suggests an inherent correlation between fast Li diffusion and thermodynamic stability arising from the configurational disorder.

Phase formation during crystallization of melts and glasses of the GaxGe40-xS60 system

The purpose of this work is to study phase formation during quenching of glass-forming melts and crystallization of GaxGe40-xS60 glasses (x = 0–15 at.%), which are promising materials for optical IR glass-ceramics. The stability against crystallization of the glasses is determined to decrease with increasing gallium content. In the case of the glass-forming melts, the stability against crystallization increases in the range x = 0–8 at.% and then decreases. It is established that, during crystallization, not pure phases of binary sulfides are formed, but their solid solutions. When quenching the melts with a gallium content of 10–15 at.%, Ga2-xGexS3 solid solutions, which are isostructural to one of the polymorphic modifications of gallium sesquisulfide, are crystallized. Solid solutions form skeletal crystals, the growth of which leads to the formation of a dendritic crystal structure. Micro-liquation in the GaxGe40-xS60 glasses is observed.

Pressure-Driven Polymorphic Transition, Emergent Insulator-To-Metal Transition, and Photoconductivity Switching in Violet Phosphorus.

Polymorphic phase transition is an essential phenomenon in condensed matter that the physical properties of materials may undergo significant changes due to the structural transformation. Phase transition has thus become an important means and dimension for regulating material properties. Herein, this study demonstrates the pressure-induced multi-transition of both structure and physical properties in violet phosphorus, a novel phosphorus allotrope. Under compression, violet phosphorus undergoes sequential polymorphic phase transitions. Concomitant with the first phase transition, violet phosphorus exhibits emergent insulator-metal transition, superconductivity, and dramatic switching from positive to negative photoconductivity. Remarkably, the resistance of violet phosphorus shows a sudden drop of around 107 along with the phase transition. In addition, piezochromism from translucent red to opaque black and suppression of photoluminescence are observed upon compression. Of particular interest is that the sample irreversibly transforms into black phosphorus with a pronounced discrepancy in physical properties from the pristine violet phosphorus after decompression. The abundant polymorphic transitions and property changes in violet phosphorus have significant implications for designing novel pressure-responsive electronic/optoelectronic devices and exploring concealed polymorphic transition materials.

Modulating Barrier Properties of Stereocomplex Polylactide: The Polymorphism Mechanism and Its Relationship with Rigid Amorphous Fraction.

The barrier properties of semicrystalline polymers are crucial for their performance and their use as packaging materials. This work uncovers the mechanism of polymorphism modification (α, α' and stereocomplex-crystals) and its combined effect on the oxygen and water vapor barrier properties of semicrystalline stereocomplex polylactide (SCPLA). A polymorphic selective filler-type nucleator was employed to eliminate the temperature effect on the development of polymorphism and rigid amorphous fraction (RAF), allowing correlations of barrier properties with different crystal forms and RAF combinations under the same amorphous composition (SCPLA). The oxygen and water vapor barrier performances strongly correlated with crystallinity and crystal form but were not monotonically related to the RAF quantity. The study proposes that the chain conformation of intermediate phases between the crystalline and amorphous phases differs with the associated crystal forms, thereby leading to different RAF "qualities" and contributing to different gas diffusion and solubility coefficients of the amorphous regions. RAF's per unit excess free volume may be varied with crystal forms, for instance: α' ≫ SC > α. Therefore, SCPLA with α' crystals exhibited high oxygen and water vapor permeabilities. Those with high SC and α crystals showed similar barrier behaviors governed by Henry's law dissolution and followed a linear "two-phase" relationship with total crystallinity.

Thermodynamic Origin of Negative Thermal Expansion Based on a Phase Transition-Type Mechanism in the GdF3-TbF3 System.

Multicomponent fluorides of rare earth elements (REEs-R) are phase transition-type negative thermal expansion (NTE-II) materials. NTE-II occurs in RF3-R'F3 systems formed by "mother" single-component dimorphic RF3 (R = Pm, Sm, Eu, and Gd) with a giant NTE-II. There are two structural types of RF3 polymorphic modifications: low-temperature β-YF3 (β-) and high-temperature LaF3 (t-). The change in a structural type is accompanied by a density anomaly: a volume of one formula unit (Vform) Vβ- >Vt-. The empirical signs of volumetric changes ΔV/V of NTE-II materials were considered. For the GdF3-TbF3 model system, an "operating-temperature window ΔT" and a two-phase composition of NTE-II materials follows from the thermodynamics of chemical systems: the phase rule and the principle of continuity. A necessary and sufficient sign of NTE-II is a combination of polymorphism and the density anomaly. Isomorphism in RF3-R'F3 systems modifies RF3 chemically by forming two-component t- and β- type R1-xR'xF3solid solutions (ss). Between the two monovariant curves of ss decay, a two-phase area with ΔTtrans > 0 (the "window ΔT") forms. A two-phase composite (t-ss + β-ss) is an NTE-II material. Its constituent t-ss and β-ss phases have different Vform corresponding to the selected T. According to the lever rule on a conode, Vform is calculated from the t-ss and β-ss compositions, which vary with T along two monovariant curves of ss decay. For the GdF3-TbF3 system, ΔV/V = f(T), ΔV/V = f(ΔT) and the "window ΔT" = f(x) dependencies were calculated.

QUASIBINARY SYSTEM Ag7PSe6– Ag2Se

Semiconductor binary and ternary argentum selenides are of considerable practical interest, particularly as promising thermoelectric materials. These include Ag2Se, a narrow-band semiconductor, and Ag7PSe6, with a disordered cationic sublattice and a rigid anionic framework that causes efficient phonon scattering. Doping of Ag7PSe6 with the narrow bandgap semiconductor Ag2Se should increase its conductivity and Ag2Se with a more disordered Ag7PSe6 argyrodite phase to a decrease in thermal conductivity. In both cases, this should increase the thermoelectric figure of merit of the respective phases. At the same time, establishing the conditions for obtaining doped phases requires studying the conditions of their existence in the Ag7PSe6-Ag2Se system. Present work studies phase equilibria in the Ag7PSe6-Ag2Se system in the entire concentration range. A corresponding phase diagram was constructed based on the X-ray phase and differential thermal analysis results. It was found that the Ag7PSe6-Ag2Se system is quasi-binary. It is characterized by four processes: two eutectoid processes at 405 K and 433 K, caused by the presence of two polymorphic modifications in Ag2Se and Ag7PSe6, respectively; eutectic process at 893 K (the coordinates of the eutectic point are 893 K and ~8 mol% Ag2Se) and monotectic process at 977 K. Above this temperature, in the concentration range of ~9 - ~87 mol%, a region of immiscibility in the liquid is observed. The homogeneity regions of the initial components are less than 5 mol%.
 Keywords: quasibinary system; selenides; phase equilibria; phase diagram.