Phase Transition Path Research Articles

Strain-mediated phase transition of MoTe2 monolayer

MoTe2 has emerged as a promising candidate in the field of integrated circuits, memristive devices, and catalysts, owing to its polymorphic nature across different phases. Experimentally, strain engineering has been demonstrated as an effective approach for manipulating the phase transition of MoTe2, but the mechanism remains unclear. The strain-dependent phase transition and its micro-mechanisms have been investigated based on first principle calculations. As demonstrated, critical strain and phase transition path from H → T′ phases are strongly governed by the applied strain's orientation, magnitude, and triaxiality. At the atomic level, nonzero movements of Te atoms within the phase transition domain with mechanical unloading have been clarified, together with an advanced understanding on the impact of strain on Te-vacancies migration. These insights advanced the knowledge of MoTe2 phase transition behavior and demonstrated the large space to explore potential applications through strain, defect, and phase engineering.

Effect of micro-diamond and nano-polycrystalline diamond interfacial microstructure on OLC phase transition

The interfacial microstructure of micro-diamond and nano-polycrystalline diamond (nPCD), as well as their effect on the phase transition of complete structure onion-like carbon (OLC), were investigated using molecular dynamics simulations and experimental methods under high pressure and temperature (HPHT). Introducing micro-diamond disrupted the symmetric equilibrium structure of complete structure OLC, reduced the diamond nucleation process, and formed a coherent interface ((111)CD // (002)Gr), where cubic diamond (111) crystal plane was parallel to graphite (002) crystal plane. This transformed the initial diffusionless phase transition path of complete structure OLC into a low potential path for phase transition along the graphite crystal direction [002] by (111)CD // (002)Gr, thereby reducing the phase transition conditions. Additionally, due to different stacking orders or breakages in the graphite layers of the complete structure OLC, micro-diamond, and nPCD formed four interfacial microstructures containing twin boundaries (TB), cubic diamond, stacking fault (SF), and amorphous grain boundary (aB). Furthermore, under HPHT effects, numerous TBs and SFs were generated inside micro-diamonds as well as at their edges, resulting in a Vickers hardness of 167 GPa for polycrystalline diamond (PCD) composite. This simple yet effective method reduces synthesis conditions for OLC precursors while producing high-performance PCD composites with promising applications.

Calculating the Soil Freezing Characteristic Curve of Saline Soil With Equivalent State of Bulk Solution

AbstractThe relationship between unfrozen water content and temperature, called as soil freezing characteristic curve (SFCC), is of importance for hydrologic, engineering, environmental issues related to frozen soil. The SFCC of saline soil is essentially a result of phase equilibrium of pore solution, which is similar but not identical to that of bulk solution. However, there is still a vacancy of study on the phase equilibrium of pore solution in frozen soil. In this study, image transformation was used to establish the relationship of phase equilibrium between bulk solution and pore solution, with four introduced parameters. Then, the new model of SFCC for saline soil was proposed based on the equivalent state of bulk solution with Pitzer model and SFCC of nonsaline soil. The model was validated by the experimental data from published articles and showed good performance in calculating SFCC of saline soils regardless of soil type, phase transition path, and soil initial water‐salt condition, and some advantages when compared to other three models. All the four introduced parameters have clear physical meanings and their relationships with soil type and initial salt concentration were discussed. Finally, the evolution of phase diagram from bulk solution to pore solution at icing stage was figured out. Further studies are needed for their relationship at salt crystallization stage. Shifting the research perspective from unfrozen water content to pore solution, this study gives a new approach to research of freezing characteristic of saline soil and could promote hydrological and engineering research in cold regions.

High-pressure and high-temperature modulation of one-dimensional infinite chain in SeO2

The structural evolution of lone-pair compounds under high-pressure and high-temperature conditions has been a subject of fundamental interest in revealing modulated polymorphs. As one of the archetypal lone-pair compounds, selenium dioxide (SeO2) has attracted much attention due to the pressure modulation of its one-dimensional infinite W-shaped chain arrangement. Here, through swarm intelligence algorithm in conjunction with the first-principles simulation, we propose the existence of an orthorhombic Pnma-SeO2 structure, characterized by V-shaped chains interconnected via vertex-sharing SeO3 pyramids. These V-shaped chains demonstrate reduced compressibility along their chain direction compared to the W-shaped chains. Calculations indicate that Pnma-SeO2 is a semiconductor with a large indirect bandgap of 2.39 eV. Remarkably, we synthesized the predicted Pnma-SeO2 in a laser-heated diamond anvil cell at a pressure of 48.5 or 87 GPa as identified by in situ synchrotron x-ray diffraction data. Our findings lead to a significant extension of the phase diagram and transition path of SeO2 and provide key insights into understanding the pressure modulation in lone-pair compounds.

Engineering of the Fano resonance spectral response with non-Hermitian metasurfaces by navigating between exceptional point and bound states in the continuum conditions.

We address the engineering of Fano resonances and metasurfaces, by placing it in the general context of open non-Hermitian systems composed of coupled antenna-type resonators. We show that eigenfrequency solutions obtained for a particular case of scattering matrix are general and valid for arbitrary antenna radiative rates, thanks to an appropriate transformation of parametric space by simple linear expansion and rotation. We provide evidence that Parity-Time symmetry phase transition path and bound states in continuum (BIC) path represent the natural axis of universal scattering matrix solutions in this parametric coupling-detuning plane and determine the main characteristics of Fano resonance. Specifically, we demonstrate the control of asymmetry and sharpness of Fano resonance through navigation between BIC and PT-symmetric phase transition exceptional point. In particular, we demonstrate a fully symmetric Fano resonance in a system of two coupled bright and dark mode resonators. This result goes beyond current wisdom on this topic and demonstrates the universality of scattering matrix eigenfrequency solutions highlighted in our study. The validity of our approach is corroborated through comparison with experimental and full 3D numerical simulations results published in the literature making it thus possible to grasp a large body of experimental work carried out in this field. The detrimental impact of absorption losses on the contrast of the Fano resonance, which must be two orders of magnitude lower than the radiative losses, is also evidenced.

In Situ Study of Purified Phase Transition Path for α‐FAPbI3 Crystallization

AbstractPhase transition during annealing in the two‐step sequential deposition has drawn intensive attention as its significance in fabricating superior perovskite films. However, previous works have not paid enough attention to the importance of the purified phase transition path in the crystallization process. Herein, different from the mixed paths in the conventional cognition, purified phase transition path for α‐FAPbI3 crystallization is achieved by introducing dimethylurea (DMU) into lead iodide (PbI2) precursor solution. The multifunctional molecule is found to design a penetrable porous PbI2 film and fundamentally regulate the perovskite crystallization by forming single phase transition path via the complete δ‐phase during annealing of perovskite. The role of DMU in purified transition path for α‐FAPbI3 crystallization is unraveled with in situ photoluminescence and grazing incidence wide‐angle x‐ray scattering (GIWAXS) investigation. The crystal quality of perovskite films is significantly improved, resulting in single crystal‐like film. The best‐performing perovskite solar cells (PSCs) deliver a power conversion efficiency of 24.75%, resulting from the higher FF of 83.25% and an improved long‐term stability up to 3600 h. This work highlights the importance of purified phase transition path for the superior crystal quality toward high‐performance perovskite photovoltaics.

Exploiting phase transitions in catalysis: reaction of and on doped -polymorphs

is well known for its reversible transition between two phases with tetragonal rutile and monoclinic structure. In a previous theoretical study (Stahl and Bredow 2022 ChemPhysChem 23 e202200131) we showed that the adsorption energy of CO is different on surfaces of the two Mo-stabilized polymorphs. This can be exploited to promote catalytic reactions by removing CO from the catalyst surface. As proof-of-principle, we investigated the hydrogenation reaction of . For this purpose, the adsorption energies of and possible intermediates and products , HCOOH, and CO were calculated. Significant differences were found for the reaction energies of the hydrogenation of to formic acid and formaldehyde on the two polymorphs. This shows that it is in principle possible to alter the reaction thermodynamics by applying reaction conditions which stabilize a particular polymorph. In order to investigate the influence of the polymorph on kinetic properties, the reactions barriers of a step-wise reaction of was calculated using the nudged elastic band method. was found to reduce the reaction barriers compared to the gas phase. Additionally, the minimum energy path of the bulk phase transition of undoped was calculated using the distinguished reaction coordinate method. A catalytic cycle exploiting the phase transition is proposed based on the theoretical results.

Influence of iron anisotropy on phase transition near grain boundary under shock

As is well known, iron plays an important role in the fields of national defense and industry, so it is of great significance to study its behavior under dynamic high pressure. As one of the most common defects in metals in nature, grain boundaries have an important influence on the mechanical properties and deformation of materials under shock. This work intends to use large-scale non-equilibrium molecular dynamics simulation to study the influence of iron anisotropy on the phase transition in bicrystal under shock loading. By tracking the local structure, shear stress distribution and morphology characteristics after shock on both sides of the grain boundaries, the factors affecting the response on both sides of the grain boundary are analyzed. Our research result shows that shocking along the non-centrosymmetric grain direction can cause significant differences in the phase transition threshold, path and mode on both sides of the symmetric grain boundary. Especially, the different phase transition dynamic processes on both sides of the sigma11 grain boundary are discussed in detail in this work, which have been rarely discussed in previous studies. Considering the symmetry of the microstructure on both sides of this type of grain boundary, the result of asymmetric shock response is different from people’s inertial cognition. Finally, it is found that the atoms in both models will shift along the direction perpendicular to the shocked direction under shock, indicating that the shock wave generated by the piston method should no longer be simply regarded as one-dimensional when shocked along the non centrosymmetric crystal direction, and the displacement of atoms along the direction perpendicular to the shocked direction is closely related to the symmetry of the crystal, which causes significant differences in shear stress on both sides of the grain boundary and ultimately affects the shock response. This study reveals that the anisotropy of lattice has an important effect on the phase transition on both sides of grain boundaries under shock loading, which can provide theoretical support for the experimental studies of polycrystalline metals and alloys under shock.

Kinetical phase transition paths and phase stability in ferroelectric HfO2

Novel ferroelectric HfO2 films have obtained great attention owing to their super advantages in electronic applications. However, the phase transition paths and ferroelectric phase stability in HfO2 still remain elusive, represented by several contradictions in theoretical and experimental results. Based on kinetical calculations on the premise of crystal axis mapping relationship rules, we systematically study the transition paths and illustrate the kinetical process in HfO2 film during the cooling process. We find two paths with the same low energy barriers from tetragonal phase transforming to orthorhombic phase. Their polarization axes are exactly orthogonal, predicting 90° domain formation at the beginning of stage of new nucleus formation. This might explain the existence of high-proportioned 90° domains in HfO2 films. Furthermore, the impact of Zr doping concentration on the stabilization of ferroelectric phase is investigated, revealing the mechanism for 50 % doping concentration as the best condition to induce ferroelectricity in HfO2.

First-principles calculation of various phase transition in Al–Sc system

Sc as one of the most important microalloying elements in advanced Al alloys has gained tremendous attentions in recent years. The newly identified Sc-rich clusters demonstrate new strengthening effect in Al alloys and thus entail a comprehensive understanding on their phase relationship. In this work, various phase transitions of binary Al–Sc system are systematically investigated by first-principles calculation together with cluster expansion. The results show the phase transition from FCC Al to HCP Sc bypass a BCC structure as a function of Sc concentration. The ordered BCC lattice experiences BCC to FCC, BCC to HCP and BCC to ω phase transitions through the Bain, Burgers and ω phase transition paths, respectively. The possibility of those phase transitions is evaluated from the calculated energy landscape along the transition paths. BCC to FCC and BCC to ω phase transitions are energetically more favorable in Al–Sc system. The bonding electron density and effective cluster interaction suggests the Al–Sc interactions play a key role in individual phase transition at different Sc concentration.

Effects of lattice distortion and amount of d electrons on the pressure-driven structural phase transition in ZnO: A comparative study of V-, Mn-, and Co-doped ZnO

The pressure-driven phase transition from fourfold würtzite (B4) to sixfold coordinated rock salt (B1) structure in ZnO, in particular in transition metal (TM) doped ones, exhibited very scattered results and remained as an outstanding issue. The in situ angle-dispersive x-ray diffraction revealed that TM doping can result in significant reduction on the onset pressure at which the pressure-driven B4-to-B1 phase transition starts to emerge, albeit the transition path appeared to be very much dependent on the doping transition metal element. Systematic comparisons on a series of V-, Mn-, and Co-doped ZnO materials indicated that, in addition to ionic sized difference-induced lattice distortion, the amount of the 3d electrons carried by the doped TM atom may also play a prominent role in the underlying mechanism of the pressure-driven phase transition. Specifically, the existence of 3d electrons may have resulted in increased screening of the Coulomb forces between the cations at increasing pressure, leading to significant softening of the c44 and c66 elastic constants, which, in turn, lowers the onset pressure in triggering the B4-to-B1 phase transition in ZnO. Our results also indicate that the initial lattice distortion induced by the ionic size difference may change the landscape of energy barrier and alter the phase transition path.

Crystal facet-dependent reduction behavior of α-Fe2O3 in hydrogen atmosphere

The reduction of α-Fe2O3 is significant in heterogeneous catalysis. However, due to the changeable crystal phase and the transformation of crystal facet, its reduction mechanism still needs further clarification. In this work, α-Fe2O3 rhombohedra, hexagonal-plate and pseudo-cubic with the facets of (104), (001) and (102) respectively were synthesized, and the evolutions of α-Fe2O3 structures during H2 reduction were investigated by multiple means including in-situ XRD. It found that the reduction of α-Fe2O3 showed a facet-dependent behavior in H2 atmosphere, that is different facets exhibited completely different rates and phase transition pathways. Specifically, the Fe2O3 (104) and Fe3O4 (220) had the fastest reduction rate in α-Fe2O3 → Fe3O4 and Fe3O4 → α-Fe, respectively, which was attributed to the higher concentration of oxygen vacancies on the corresponding crystal facets. The phase transition paths for Fe2O3 (102) and Fe2O3 (104) were α-Fe2O3 → Fe3O4 → α-Fe, while Fe2O3 (001) was α-Fe2O3 → Fe3O4 → FeO → α-Fe. Additionally, DFT calculations further revealed that Fe2O3 (104) and Fe3O4 (220) had lower interaction energy between O and Fe atoms and easily formed oxygen vacancy. Consequently, these facets presented different formation rates of H2O, leading to significant differences in the phase transition process.

Pressure-induced phase transitions in Ni-bearing ferrosilite (Ni-En31Fs65)

Abstract Orthopyroxene is an abundant mineral in subducting slabs. Studying its phase transitions at high pressure is important to the understanding of mineralogy of subducting slabs in the deep Earth. Synchrotron-based single-crystal X-ray diffraction experiments were conducted on a synthetic Ni-bearing ferrosilite (Ni-En31Fs65) at pressures up to 33.8 GPa. Three phase transitions were observed at 12.1(6), 15.6(6), and 31.3(25) GPa. The first two phase transitions in Ni-En31Fs65 resemble the previously described phase transitions in Ni-free Fe-rich orthopyroxenes, i.e., the initial α-opx (Pbca) transforms to β-opx (P21/c), then the latter transforms to γ-opx (Pbca). This indicates that the incorporation of a few mol% NiSiO3 does not influence the phase transition path of Fe-rich orthopyroxene. After the third phase transition, the structure (P21ca) of Ni-En31Fs65 resembles the previously reported β-popx observed in En90 at high pressure, although the onset pressure of the phase transition in Ni-En31Fs65 is ~7 GPa lower than that in En90. β-popx has a post-pyroxene structure that contains fivefold- and sixfold-coordinated Si cations. Our results indicate that the post-pyroxene structure is β-popx (P21ca) for either Fe-poor or Fe-rich orthopyroxenes, although the phase transition path before the pyroxene → post-pyroxene is compositionally dependent. Additionally, unlike the second and third transitions, whose onset pressures are monotonously decreased by increasing Fe content, the Fe effect on shifting the first transition is much more significant for orthopyroxenes within En <50 mol% than that within En >50 mol%.

Phase stability behavior of (Ti,Al,Si)N multi-principal nitrides regulated by the Si content: Thermodynamics and first principles calculations

The cubic (B1) (rock salt-type) Ti(1−x)AlxN system is one of the most important protective coatings in industry due to properties such as hardness and thermal stability. Moreover, different alloying elements have been studied to increase its working temperature. Silicon has been demonstrated as an interesting option, since it can improve the oxidation resistance and stabilize the system in the hexagonal (B4 wurtzite-type) phase. Different experimental studies have been developed to understand the role of Si in the conformation of Ti(1−x-y)AlxSiyN pseudo-ternary coatings. However, some results seem to be contradictory. Here, we used ab initio and CALPHAD calculations to understand the Si incorporation effects on the phase stability and the critical Si composition. We found that the maximum mixing enthalpy for B1 falls on the TiN-AlN side of the ternary diagram and continues until almost equimolar composition. The B1-B4 phase transition point shifted significantly from x(AlN) = 0.71 without Si to x(AlN) = 0.21 with x(SiN) = 0.4. The critical composition of x(SIN) = 0.06 was found, where the miscibility gap region increased, demonstrating unfavorable results if going higher in Si content.The ab-initio calculations showed that the inclusion of silicon reduced the mechanical properties of the B1 phase, but at the critical threshold of 10 at% of silicon content, the mechanical properties did not significantly diminished. Calculated diagrams at equilibrium conditions mapped out the phase evolution to determine the phase transition paths and phase dependence on common coating deposition parameters. These results could serve as a reference for the experimental obtaining of improved hard coatings based on the (Ti,Al,Si)N multi-principal nitride.

Mineralogy and phase transition mechanisms of atmospheric mineral particles: Migration paths, sources, and volatile organic compounds

Inorganic mineral particles play an important role in the formation of atmospheric aerosols in the Sichuan Basin. Atmospheric haze formation is accompanied by the phase transition of mineral particles under high humidity and stable climatic conditions. Backward trajectory analysis was used in this study to determine the migration trajectory of atmospheric mineral particles. Furthermore, Positive matrix factorization (PMF) was used to analyze the sources of atmospheric mineral particles. The phase transition mechanisms of atmospheric mineral particles were studied using ion chromatography, inductively coupled plasma emission spectrometry, total organic carbon analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive spectrometry, and grand canonical Monte Carlo methods. Three migration and phase transition paths were identified for the mineral particles. Sources of atmospheric mineral particles included combustion, vehicle emissions, industrial emissions, agricultural sources, and mineral dust. The main mineral phases in atmospheric particles, calcite and dolomite, were transformed into gypsum, and muscovite may be transformed into kaolinite. The phase transition of mineral particles seriously affects the formation of aerosols and worsens haze. Typically, along the Nanchong-Suining-Neijiang-Zigong-Yibin path, calcite is converted into gypsum under the influence of man-made inorganic pollution gases, which worsen the haze conditions and cause slight air pollution for 3–5 days. However, along the Guangyuan-Mianyang-Deyang-Chengdu-Meishan-Ya'an path, anthropogenic volatile organic compounds (VOCs) hindered gypsum formation from dolomite. Furthermore, dolomite and VOCs formed stable adsorption systems (system energies from −0.41 to −4.76 eV, long bonds from 0.20 to 0.24 nm). The adsorption system of dolomite and m/p-xylene, with low system energy (−1.46 eV/−1.33 eV) and significant correlation (r2 = 0.991, p < 0.01), was the main cause of haze formation. Consequently, calcite gypsification and dolomite–-VOC synergism exacerbated regional haze conditions. This study provides a theoretical reference for the mechanism of aerosol formation in basin climates.

Salt Hydrate Adsorption Material-Based Thermochemical Energy Storage for Space Heating Application: A Review

Recent years have seen increasing attention to TCES technology owing to its potentially high energy density and suitability for long-duration storage with negligible loss, and it benefits the deployment of future net-zero energy systems. This paper provides a review of salt hydrate adsorption material-based TCES for space heating applications at ~150 °C. The incorporation of salt hydrates into a porous matrix to form composite materials provides the best avenue to overcome some challenges such as mass transport limitation and lower thermal conductivity. Therefore, a systematic classification of the host matrix is given, and the most promising host matrix, MIL-101(Cr)(MOFs), which is especially suitable for loading hygroscopic salt, is screened from the perspective of hydrothermal stability, mechanical strength, and water uptake. Higher salt content clogs pores and, conversely, reduces adsorption performance; thus, a balance between salt content and adsorption/desorption performance should be sought. MgCl2/rGOA is obtained with the highest salt loading of 97.3 wt.%, and the optimal adsorption capacity and energy density of 1.6 g·g−1 and 2225.71 kJ·kg−1, respectively. In general, larger pores approximately 8–10 nm inside the matrix are more favorable for salt dispersion. However, for some salts (MgSO4-based composites), a host matrix with smaller pores (2–3 nm) is beneficial for faster reaction kinetics. Water molecule migration behavior, and the phase transition path on the surface or interior of the composite particles, should be identified in the future. Moreover, it is essential to construct a micromechanical experimental model of the interface.

Effect of residual carbon on the phase transformation and microstructure evolution of alumina-mullite fibers prepared by sol-gel method

Sol-gel method, as one of the most effective methods, has been widely used in producing high-property ceramics. In this method, the pyrolysis of precursor significantly influences the following microstructure evolution and properties of ceramic materials. In this work, the effect of residual carbon, influenced by the pyrolysis atmosphere, on the phase transition and microstructure evolution of the alumina-mullite fibers was investigated. It was revealed that the phase transition path of the preheated fibers with 0.53 wt% residual carbon was amorphous phase → aluminosilicate → tetragonal mullite → orthorhombic mullite + θ-Al2O3. The phase transition path of the preheated fibers with 10.51 wt% residual carbon became amorphous phase → γ-Al2O3 → orthorhombic mullite + α-Al2O3 + θ-Al2O3. In addition, the residual carbon contributes to improve the densification of alumina-mullite fibers and refine the fiber grain size. The effect of residual carbon on the formation of mullite coarse grains was further discussed.

Reconfiguring Sodium Intercalation Process of TiS2 Electrode for Sodium-Ion Batteries by a Partial Solvent Cointercalation

Titanium disulfide (TiS2), a first-generation cathode in lithium batteries, has also attracted a broad interest as a sodium-ion battery electrode due to fast sodium intercalation kinetics and large theoretical capacity. However, the reversibility of sodium de/intercalation is far inferior to that of lithium because of the unfavorable intermediate phase formation. Herein, we demonstrate that reconfiguring sodium intercalation via partial solvent cointercalation alters the phase-transition paths for the entire reactions of NaxTiS2 (0 < x < 1), detouring the formation of the unfavorable intermediates. Additionally, it unexpectedly results in a remarkable enhancement of sodium intercalation reversibility, boosting the cycle stability (1000 cycles) accompanying high power capability (10C rate). Comparative investigations reveal that the sodium intercalation in ether-based electrolyte involves a preintercalation of solvent molecules, which is subsequently dissimilar to the bare sodium intercalation in conventional electrolytes. Rediscovery of the intercalation behavior of TiS2 offers a new insight in revisiting the reversibility and kinetics of the commonly known electrodes for batteries.

Theoretical model for the Mpemba effect through the canonical first-order phase transition.

The Mpemba effect is the phenomenon in which the system with high initial temperature cools faster than the system with low initial temperature when all other conditions are the same. A theoretical model of the Mpemba effect through the canonical first-order phase transition is proposed in this paper, which shows that in the cooling processes, the path of the first-order phase transition of the system with the high initial temperature does not pass through any metastable state, while the path of the first-order phase transition of the system with the low initial temperature passes through a metastable state, which leads to the occurrence of the Mpemba effect. Then an example of the theoretical model is given in the Blume-Emery-Griffiths model. The Monte Carlo algorithm is adopted to calculate the estimated times for both systems with different initial temperature to cool down and undergo a first-order phase transition. The simulation results demonstrate a Mpemba effect in the system. Moreover, the evolution paths of the first-order phase transitions of the systems with high and low initial temperatures are given, respectively. The theoretical model presented here may help explain the Mpemba effect in water.

Various Approaches to Studying the Phase Transition in an Octamethylcyclotetrasiloxane Crystal: From X-ray Structural Analysis to Metadynamics

The structure, thermodynamic parameters, and the character of thermal motion in octamethylcyclotetrasiloxane (D4) were investigated using the combination of experimental (single-crystal X-ray diffraction, thermochemistry) and theoretical (density functional theory calculations, ab initio molecular dynamics and metadynamics) methods. Single crystals of D4 were grown in a glass capillary in situ and the structures of high- (238–270 K) and low-temperature (100–230 K) phases were studied in detail. In the temperature interval 230–238 K, a phase transition with rather low enthalpy (−1.04(7) kcal/mol) was detected. It was found that phase transition is accompanied by change of conformation of cyclosiloxane moiety from boat-saddle (cradle) to chair. According to PBE0/6-311G(d,p) calculation of isolated D4, such conformation changes are characterized by a low barrier (0.07 kcal/mol). The character of molecular thermal motion and the path of phase transition were established with combination of periodic DFT calculations, including molecular dynamics and metadynamics. The effect of crystal field led to an increase in the calculated phase transition barrier (4.27 kcal/mol from low- to high-temperature phase and 3.20 kcal/mol in opposite direction).