Phase Transition Path Research Articles

The pressure-induced phase transition studies of In2S3 and In2S3:Ce nanoparticles

A novel method, gas–liquid phase chemical deposition is developed to prepare In2S3 and In2S3:Ce nanoparticles. The structural, morphology and composition feature of these two nanoparticles is studied by XRD, HRTEM, and XPS. In situ high-pressure synchrotron X-ray diffraction studies were carried out by using a diamond-anvil cell. The doping does not influence the tetragonal-to-cubic phase transition path while results in a lower phase transition pressure of In2S3:Ce nanoparticles (4.3GPa) than that of In2S3 nanoparticles (7.1GPa). The bulk moduli of tetragonal phases are B0=87.1±4.3GPa and B0=55.6±4.1GPa, respectively. The distinct high-pressure behaviors can be explained in term of the doped ions, causing lattice distortion and reducing structural stability of the In2S3 nanoparticles and further accelerating the phase transition.

Phase-Transition Induced Elastic Softening and Band Gap Transition in Semiconducting PbS at High Pressure

We have investigated the crystal structure and phase stability, elastic incompressibility, and electronic properties of PbS based on high-pressure neutron diffraction, in-situ electrical resistance measurements, and first-principles calculations. The refinements show that the orthorhombic phase is structurally isotypic with indium iodide (InI) adopting a Cmcm structure (B33). The cubic-to-orthorhombic transition occurs at ∼2.1(1) GPa with a 3.8% volume collapse and a positive Clausius-Clapeyron slope. Phase-transition induced elastic softening is also observed, which is presumably attributed to the enhanced metallic bonding in the B33 phase. On the basis of band structure simulations, the cubic and orthorhombic phases are typical of direct and indirect semiconductors with band gaps of 0.47(1) and 1.04(1) eV, respectively, which supports electrical resistivity measurements of an abrupt jump at the structural transition. On the basis of the resolved structure for B33, the phase transition paths for B1→B33→B2 involve translation of a trigonal prism in B1 and motion of the next-nearest neighbor Pb atom into {SPb7} coordination and subsequent lattice distortion in the B33 phase.

Structural relationships between single atom type crystal structures and intermetallic compound structures, as illustrated by Laves‐ and Hume‐Rothery phases

In comparison to the single atom type crystal structures, which are relatively simple and are concentrated in four types of structure (Cu, W, Mg, diamond), the crystal structures of intermetallic phases are manifold and often very complicated. At first sight there is no obvious connection between these types of crystal structures, however, a transition mechanism must exist for the solid‐state transition from the simple single atom type crystal structures to the intermetallic phase structures. Such a mechanism would show the inner connection between the structures. In this work the topic is dealt with from a crystallographic point of view. The transition between the structures can be described by the three steps (1) substitution of atoms, (2) systematically ejection of particular atoms from the emerging intermediate structure and (3) spatial relaxation especially of the atoms around the newly formed interstices. This general structural phase transition path will be discussed for two of the intermetallic classes, the Laves phases and the Hume‐Rothery phases. A suitable way of showing this is by making a comparison between the coordination polyhedra (atomic environments) of the single atom type crystal structures and those of the derived intermetallic crystal structures.

Direct Observation of a Metastable Crystal Phase of LixFePO4 under Electrochemical Phase Transition

The phase transition between LiFePO4 and FePO4 during nonequilibrium battery operation was tracked in real time using time-resolved X-ray diffraction. In conjunction with increasing current density, a metastable crystal phase appears in addition to the thermodynamically stable LiFePO4 and FePO4 phases. The metastable phase gradually diminishes under open-circuit conditions following electrochemical cycling. We propose a phase transition path that passes through the metastable phase and posit the new phase's role in decreasing the nucleation energy, accounting for the excellent rate capability of LiFePO4. This study is the first to report the measurement of a metastable crystal phase during the electrochemical phase transition of LixFePO4.

TiO2아나타제에 대한 고압 상변이 연구

<TEX>$TiO_2$</TEX>의 동질이상체 중 하나인 아나타제는 고압 하에서 결정의 크기와 모양에 따라 다른 상변이 경로를 보이는 것으로 알려져 있다. 본 실험에 이용된 아나타제 분말시료는 15~25 nm 정도 크기의 입자로 구성되어 있으며, 고압라만분광분석 결과와 고압 X-선회절실험결과 분석을 종합하면 20 GPa 이상의 압력에서 비정질로 상변이하는 것으로 관찰되었다. 상온에서 압력의 영향으로 상변이한 비정질 구조는 압력을 제거하여도 출발 결정구조로 회귀하지 않는 것으로 밝혀졌다. 이 결과는 베델레이트로 상변이하는 이전의 결과와 상치되며, 출발시료 구성입자의 분급상태가 입자의 불안정성에 영향을 끼쳐 최종적으로 비정질화에 기여한 것으로 판단된다. Anatase, one of the <TEX>$TiO_2$</TEX> polymorphs, is known to show different phase transition paths depending on its crystalline and shape. Particle size of 15~25 nm anatase has been subjected to high-pressure Raman spectroscopy and X-ray diffraction studies using a diamond anvil cell. We observe that the starting sample transforms to an amorphous phase above approx. 20 GPa, which is retained upon pressure release to ambient condition. This is in contrast to previously established transition to baddeleyite phase and we suspect difference in the particle distribution state trigger phase instability of nanoparticles and hence amorphization.

First-principles study of doping effect on the phase transition of zinc oxide with transition metal doped

Zinc oxide (ZnO) is a promising material for its wide application in solid-state devices. With the pressure raised from an ambient condition, ZnO transforms from fourfold wurtzite (B4) to sixfold coordinated rocksalt (B1) structure. Doping is an efficient approach to improve the structures and properties of materials. Here we use density-functional theory (DFT) to study doped ZnO and find that the transition pressure from B4 phase to B1 phase of ZnO always decreases with different types of transition metal (V, Cr, Mn, Fe, Co, or Ni) doped, but the phase transition path is not affected by doping. This is consistent with the available experimental results for Mn-doped ZnO and Co-doped ZnO. Doping in ZnO causes the lattice distortion, which leads to the decrease of the bulk modulus and accelerates the phase transition. Mn-doped ZnO shows the strongest magnetic moment due to its half filled d orbital. For V-doped ZnO and Cr-doped ZnO, the magnetism is enhanced by phase transition from B4 to B1. But for Mn-doped ZnO, Fe-doped ZnO, Co-doped ZnO, and Ni-doped ZnO, B1 phase shows weaker magnetic moment than B4 phase. These results can be explained by the amount of charge transferred from the doped atom to O atom. Our results provide a theoretical basis for the doping approach to change the structures and properties of ZnO.

Order–order phase transition and transformation in co-assembled particles from fluorinated FA/FB type diblock copolymers

Co-assembly of poly(tert-butylacrylate)-b-poly(2-[(perfluorononenyl) oxy] ethyl methacrylate) (PtBA-b-PFNEMA, FA) and poly(ethyleneoxide)-b-poly(2-[(perfluorononenyl) oxy] ethyl methacrylate) (PEO-b-PFNEMAs, FB) were carried out to construct binary blend polymeric particles with diverse microphase structures through fluorophilic interaction. Successful control of the phase behavior relies on the location of FB within a nanoscale particle. Due to the fluorophilic interaction, FB is located at the interface between PtBA and PFNEMA or partly dissolved in the PFNEMA phase rather than forming an individual microdomain. By changing the composition of the binary blend particles, the water content, and preparation temperature and the fluorophilic interaction could be tuned and hence the location of FB could be influenced. Order–order phase transition and transformation from most stable onion-like lamellar structures to stacked lamellar structures and cylindrical structures were achieved utilizing PEO113-b-PFNEMA11 (FB1). In addition, the relatively shorter PFNEMA chain and larger dispersity (Đ) of PEO113-b-PFNEMA4 (FB2) resulted in the ubiquitously coexistence of ordered lamellar and gyroid microdomains in the same particles. These transitional structures, which were successfully obtained by both SEM and TEM, would be very useful for the investigation of the phase transition path. The introduction of fluorophilic interactions into the dynamic self-organized precipitation (D-SORP) method sustained the delicate control of the phase behavior in polymeric particles.

Tetragonal high-pressure phase of InI predicted from first principles

Ab initio particle swarm optimization algorithm for crystal structural prediction was employed to uncover the high-pressure crystal structure of indium iodide (InI). We have predicted one tetragonal high-pressure phase for InI with P4/nmm symmetry, which is energetically much superior to the previously proposed CsCl-type structure. The P4/nmm-InI possesses alternative stacking of double I and In layers. The arrangement of adjacent I and In layers of P4/nmm-InI is similar to that of the CsCl-type structure. The calculated electronic density of states supports a metallic character for this tetragonal phase that is similar to the high-pressure behavior of IIA–VIB families. Furthermore, the phase transition path from the ambient pressure TlI–InI→P4/nmm-InI has been discussed.

First-principle study of strain-driven phase transition in incipient ferroelectric SrTiO 3

First-principle calculations were carried out to investigate the epitaxial strain dependence of the structural stability and related properties of SrTiO 3. The P4mm-to-P4/mmm-to-Amm2 phase transitions in SrTiO 3 with the epitaxial strain changing from compressive to expansive have been identified by analysis of the soft-mode eigendisplacement. The zero-temperature critical strains for the P4mm-to-P4/mmm and P4/mmm-to-Amm 2 phase transitions are −0.72% and 0.83%, respectively, which is consistent with the previous predictions based on the phenomenological thermodynamic model and the parameterized total-energy model. The influences of the epitaxial strain on the dielectric tensor and spontaneous polarization along the phase transition path are discussed in terms of charge transfer. Further investigations on the vibration modes show unusual softening behaviors of the A 1 and B 2 modes in the Amm2 phase, which may be associated with the soft phonon modes away from Γ point and possibly result in other phase transitions unreported by any previous studies.

Non-equilibrium phases in the Fe–Rh system studied by ion beam mixing and ab initio calculation

In the Fe–Rh system, the Fe100−xRhx (x=40, 50, 65, 70, and 90) multilayered films were prepared and then subjected to ion beam mixing using 200keV Xe ions. Upon ion beam mixing, amorphous alloy was obtained in the Fe70Rh30 sample, in which an interesting phase transition path was observed as Fe+Rh→fcc→fcc+a→fcc+bcc→fcc. In addition, a new metastable crystalline fcc phase was observed in the Fe50Rh50 sample together with the solid solutions, and the lattice constants of the ion mixed phases were consistent with those from ab initio calculations. Possible mechanisms for the formation of both amorphous and metastable crystalline phases are discussed in terms of the atomic collision theory.

PH2O-dependent structural phase transitions in the zeolite mesolite: Real- and reciprocal-space crystal structure refinements

The response of the mesolite crystal structure (Na 16 Ca 16 Al 48 Si 72 O 240 ·64H 2 O) to dehydration was evaluated as a function of temperature and partial pressure of water (i.e., P H₂O or relative humidity, RH) using laboratory X-ray powder diffraction (XRD; CuKα radiation) and synchrotron X-ray pair distribution function (PDF) methods. At 425 °C under low-P H₂O conditions (P H₂O ≤ ~1.3 mbar), dehydrated mesolite preserved the long-range ordered aluminosilicate framework structure, which has not been previously observed. This new dehydrated phase, x-metamesolite, has unit-cell parameters [a = 16.731(3) Å, b = 17.822(2) Å, c = 6.312(1) Å, V = 1882.5(5) Å 3 , and possible space group Fdd2] similar to those of other dehydrated natrolite phases (either α1- or α2-metanatrolite). Conversely, under high-P H₂O conditions (P H₂O &gt; ~1.3 mbar), dehydrated mesolite became amorphous (amorphous T 5 O 10 ) at 425 °C. The local structure of amorphous T 5 O 10 was characterized by PDF analyses, which showed the formation of twisted T 5 O 10 nano-fibers [with dimensions (LWH) of ~6.9 × 6.9 × 6.3 Å] resulting from breakage of the mesolite aluminosilicate framework. The two distinct high-temperature P H₂O -dependent phase transition paths illustrate the importance of considering the combined effects of temperature and P H₂O in mesolite. In addition, the low-temperature phase transition in mesolite, involving order-disorder of the extraframework cations, also showed a P H₂O -dependent transition temperature. Although, there is no path dependence on P H₂O for this transition, the local arrangement of Na, Ca, and vacancies in disordered metamesolite (formed through the extraframework cation order-disorder phase transition) likely influences the thermal stability of the aluminosilicate framework during further heating.

Two new colloidal crystal phases of lipid A-monophosphate: Order-to-order transition in colloidal crystals

A study of the structure of stable regular-shaped nanocrystals of hexa-acylated (C(14)) lipid A-monophosphate from Escherichia coli was carried out using dilute electrostatically stabilized aqueous dispersions at low ionic strength (I=1.0x10(-5)M NaCl). An order-to-order transition of colloidal clusters of lipid A-monophosphate was found at two volume fractions: phi=5.9x10(-4) and phi=11.5x10(-4). The clusters belonged to the cubic space groups Pm3n and Ia3d with unit-cell dimensions of a=4.55 nm and a=6.35 nm, respectively, as revealed by small-angle x-ray diffraction and electron-diffraction results of thin nanocrystals of lipid A-monophosphate. When viewed in the scanning electron microscope these fragile clusters displayed a number of shapes: cubic, cylindrical, and sometimes-rounded hexagons, which were extremely sensitive when exposed to an electron beam. The smallest and most numerous of the clusters appeared as approximately 7 nm cubes. Crystalline cluster formation occurred over a wide volume-fraction range, between 1.5x10(-4) and 40.0x10(-4), and at temperatures of 20 and 35 degrees C. The crystalline networks of the lipid A-monophosphate clusters may be represented by space-filling models of two pentagonal dodecahedra with six tetrakaidecahedra arrangements of lipid A-"micelles" in the cubic space group Pm3n. The simulated electron density profiles are in accord with spherical clusters of lipid A-monophosphate at the corners and at the body centers of the cubic Pm3n unit cell. The profiles are rounded tetrahedrally at distances of 1/4 and 3/4 along one of the bisectors of each face of the cubic unit cell. These nanocrystalline systems provide examples of "cellular" crystalline networks, which rearrange themselves spontaneously into three-dimensional polyhedral structures. It appears that a closely related analogy exists between the tetrahedrally close-packed networks as revealed for the lipid A-mono- and diphosphates [C. A. Faunce, H. Reichelt, H. H. Paradies, et al., J. Chem. Phys. 122, 214727 (2005); C. A. Faunce, H. Reichelt, P. Quitschau, et al., J. Chem. Phys. 127, 115103 (2007)]. However, the cubic Ia3d phase consists of two three-dimensional networks of rods, mutually intertwined but not connected. For this cubic Ia3d phase each junction involves three coplanar rods at an angle of 120 degrees, showing an interwoven labyrinth of lipid A-monophosphate rods which are connected three by three. The rod diameter is approximately 2.2 nm, which is similar in diameter to the disk-shaped aliphatic chiral core of lipid A-monophosphate (2.14 nm) with an ellipticity of 0.62 seen for the "c" position of the tetrakaidecahedra in the Pm3n cubic unit cell. An epitaxial relationship appears to exist between the {211} planes of the cubic Ia3d phase and the (001) planes of the lamellar phase as well as with the {10} planes of the hexagonal phase. The transformation of the cubic into the hexagonal phase can be reconciled by the growth of a cylinderlike assembly of lipid A-monophosphate molecules of the hexagonal phase parallel to the 111 directions of the cubic Ia3d phase. Upon cooling from 35 to 20 degrees C the cubic Ia3d lipid A-monophosphate phase unexpectedly transforms and gives rise to an intermediate R3m structure (a=3.90+/-0.12 nm, c=7.82+/-0.05 nm, and gamma=120 degrees). Both cubic Ia3d and hexagonal R3m phases originate from similar rodlike units of lipid A-monophosphate clusters. However, the overall shapes of the assemblies are different because of their spatial distribution. Both assemblies morphologically bridge the lipid A-monophosphate hexagonal and and lamellar phases. The structural path followed during the phase transitions is governed by topological similarities between the phase which forms and the one from which it originates. Although the two phases, Ia3d and R3m, have similar curvature energies on cooling, the topology is more than likely to be the initial factor determining the overall phase transition path.

Phase-transition mechanism of h-BN [formula omitted]w-BN from first principles

We present ab initio calculations of the electron energy-loss near edge structure (ELNES) on hexagonal boron nitride to reveal the mechanism of its high pressure transition to wurtzite phase. Our simulated ELNES with the proposed phase-transition path of a 1/8 shift along [0001] for N atoms in h -BN is in excellent agreement with experimental data. Subsequent enthalpy calculation further confirmed the validity of this transition path. Our results support the experimental suggestion by Meng et al. [Y. Meng, H.-K. Mao, P.J. Eng, T.P. Trainor, M. Newville, M.Y. Hu, C.-c. Kao, J.F. Shu, D. Hausermann, R.J. Hemley, Nature Mater. 3 (2004) 111].

Nonadiabaticity in the iron bcc to hcp phase transformation

Iron is known to undergo a pressure-induced phase transition from the ferromagnetic (FM) body-centered-cubic (bcc) alpha-phase to the nonmagnetic (NM) hexagonal-close-packed (hcp) epsilon-phase, with a large observed pressure hysteresis whose origin is still a matter of debate. Long ago, Burgers [Physica (Amsterdam) 1, 561 (1934)] proposed an adiabatic pathway for bcc to hcp transitions involving crystal shear followed by atom shuffles. However, a quantum mechanics search in six-dimensional stress-strain space reveals a much lower energy path, where the crystal smoothly shears along the entire path while the atoms shuffle only near the transition state (TS). The energy profile for this phase transition path exhibits a cusp at the TS and closely follows bcc and hcp diabatic energy wells. Both the cusp and the overlap with diabatic energy surfaces are hallmarks of nonadiabaticity, analogous to, e.g., electron transfer (ET) reactions in liquids. Fluctuations in the positions of FM bcc iron atoms near the TS induce magnetic quenching (akin to solvent fluctuations inducing ET), which then promotes NM hcp iron formation (akin to solvent reorganization after ET). We propose that the nonadiabatic nature of this transition at the atomic scale may contribute to the observed pressure hysteresis.

Phase-Transition Plasticity Response in Uniaxially Compressed Silicon Nanospheres

We present a microscopic description for the response of crystalline Si nanospheres up to 10 nm in radius for various uniaxial compression levels. The behavior at low compressions closely resembles the Hertzian predictions. At higher compressions the creation of a new beta-tin phase in the particle core leads to (i) volumetric changes (ii) an increase in elastic moduli, and (iii) significant hardening. Further, (iv) a reversible character of the transformation is obtained with molecular dynamics simulations. The agreement of (i)-(iv) with recent experimental findings challenges the current exclusive view of a dislocation plasticity response in somewhat larger nanoparticles. The phase-transition path should dominate in ultrasmall structures, where dislocation activity is prohibited.

플라이 애쉬를 이용한 다공성 코디어라이트의 합성 및 특성

Porous cordierite was synthesized by the mechano-chemical processing using fly ash. The phase evolution of cordierite was investigated as a function of processing variables such as milling time and sintering temperature. In this study, the phase transition path of cordierite from fly ash was followed by sapprine/spinel → mullite/spinel → α-cordierite. Porous cordierite fabricated after 32 h of milling time and sintering at 1150℃ showed relatively low thermal expansion coefficient (2.5 × 10 -6 /℃ (25~1000℃)) and high porosity (75%).

Phase transition and ion conduction path in a zirconia-scandia solid solution

Phase transition and ion conduction path in a zirconia-scandia solid solution

Rietveld refinement study of the pressure dependence of the internal structural parameteruin the wurtzite phase of ZnO

The pressure dependence of the internal structural parameter $u$ of the wurtzite phase of ZnO was studied using high resolution angular dispersive x-ray diffraction up to 12 GPa in a helium pressure medium. The $u$ parameter increases with pressure up to about 0.430 at about 5.6 GPa, and then rapidly decrease to about 0.380 during the phase transition. Two models of the phase transition path were proposed recently by first-principles calculations [A. M. Saitta and F. Decremps, Phys. Rev. B 70, 035214 (2004); S. Limpijumnong and S. Jungthawan, Phys. Rev. B 70, 054104 (2004)]. These possible mechanisms responsible for the wurtzite-to-rocksalt phase transition under high pressure are experimentally evaluated based on our results. The bulk moduli of the wurtzite and rocksalt phase at zero pressure were estimated as $135.3\ifmmode\pm\else\textpm\fi{}1.8$ and $177.4\ifmmode\pm\else\textpm\fi{}4.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, respectively.

Polymorphism ofTi3SiC2ceramic: First-principles investigations

The Nanolaminate ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ ceramic exhibited unique mechanical properties, such as high modulus, low anisotropic hardness to modulus ratio and microscale ductility etc. The planar close-packed Si atoms were expected to play a dominant role in deducing these properties. By performing first-principles total energy calculations, we demonstrated that a reversible polymorphic phase transition occurred when shear strain energy was large enough to close an energy barrier. The phase transition path was described as the Si atoms sliding between $2b$ and $2d$ Wyckoff positions on the $(112\ifmmode\bar\else\textasciimacron\fi{}0)$ plane. The electronic band structure, lattice dynamics, and structure stability were discussed for the two polymorphs, respectively. We demonstrated that the $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ was more stable than $\ensuremath{\beta}\ensuremath{-}{\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ by comparing the ground-state total energy and ab initio Gibbs free energy. Raman and infrared active phonon modes were illustrated for feasibly identifying the two phases in experimental spectra. The results were used to assign peaks in the experimental Raman spectrum with distinct vibrational modes, and to clarify the origin of the uncertain peak. The calculated heat capacity and volume thermal expansion coefficient agreed with experimental values well. The elastic mechanical parameters of the polymorphs were presented and compared with respect to various strain modes. Based on electronic band structure discussions, we clarified the mechanism of anisotropic hardness of ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2},$ which attributed to different covalent bonding strengths involved in kink migration.

First-principles study of the mechanisms for the pressure-induced phase transitions in zinc-blende CuBr and CuI

The lattice dynamics of zinc-blende (ZB) CuBr and CuI is studied as a function of pressure using density functional linear-response theory. A pressure-induced soft transverse acoustic (TA) phonon mode is identified for both compounds. Each compound shows a different pressure-induced phonon softening behavior. A TA phonon branch softens along the [\ensuremath{\xi}\ensuremath{\xi} 0] direction in CuBr, resulting in a phase transition from a ZB phase (CuBr-III) to a tetragonal phase (CuBr-IV). A softening TA phonon mode at the zone boundary $L$ point in CuI may induce a phase transition from a ZB phase (CuI-III) to a rhombohedral phase (CuI-IV), although the phonon softening towards zero frequency in CuI is superseded by a first order phase transition occurring at 1.74 GPa. Possible phase transition paths are presented for both compounds.