Intermediate Mixed Phase Research Articles

A systematic study of rare‐earth ions size‐dependent structural phase transition from monazite to zircon‐type in rare earth chromates using Raman spectroscopy

AbstractRare earth chromates (RCrO4) undergo monazite to zircon‐type structural phase transition due to a decreased rare‐earth ion size. They also exhibit an intermediate mixed phase. However, there is no systematic study on the influence of structural distortion on their phononic behavior, which is quite sensitive to subtle environmental variations. A change in the room temperature phononic spectrum was studied in the family of RCrO4 compounds, where R was varied from La to Yb using Raman modes. With an increase in the atomic number from Nd to Yb for zircon‐type phases, the external translational and rotational modes were observed to shift towards lower and higher wavenumbers, respectively. At the same time, all internal vibrational modes shifted towards higher phonon energies. A comparison between Raman modes for monazite, intermediate, and zircon‐type RCrO4 phases showed a gradual shift in the internal modes towards a higher wavenumber. The confirmation of the change in Raman modes with the decreasing radius was found by comparing the rare‐earth elements in DyCrO4 and LaCrO4 with non‐rare‐earth elements in YCrO4.

Equivalence and superposition of real and imaginary quasiperiodicities

We take non-Hermitian Aubry–André–Harper models and quasiperiodic Kitaev chains as examples to demonstrate the equivalence and superposition of real and imaginary quasiperiodic potentials (QPs) on inducing localization of single-particle states. We prove this equivalence by analytically computing Lyapunov exponents (or inverse of localization lengths) for systems with purely real and purely imaginary QPs. Moreover, when superposed and with the same frequency, real and imaginary QPs are coherent on inducing the localization, in a way which is determined by the relative phase between them. The localization induced by a coherent superposition can be simulated by the Hermitian model with an effective strength of QP, implying that models are in the same universality class. When their frequencies are different and relatively incommensurate, they are incoherent and their superposition leads to less correlation effects. Numerical results show that the localization happens earlier and there is an intermediate mixed phase lacking of mobility edge.

Unraveling the Temperature Mediated Dual Band Edge in TiO2 Nanotubes with Improved Photocatalytic Property

The resurgence of photocatalytic activity of TiO2 is driven in past few decades owing to its potential to meet several contemporary global challenges, such as pollutant degradation, nonfossil fuel production from CO2, or H2 generation from aqueous solutions [1]. Among three TiO2 polymorphs anatase TiO2 (A-TiO2), rutile TiO2 (R-TiO2) and brookite TiO2, first two are the mostly investigated phases for photocatalytic application. However, the use of TiO2 photoelectrodes is limited owing to the recombination of photo-generated (e-h) pairs in the bulk, and also at the electrode/electrolyte interface. The overall efficiency associated with A-TiO2 is still considered to be higher with respect to R-TiO2 due to higher charge carrier mobility and slower charge recombination kinetics [2].Nevertheless, proper ratio of anatase-rutile phases (Degussa P25) is superior in photocatalytic activity than that of pure rutile or anatase phase. On the other hand, anodic TiO2 nanotubes TNTs have attracted wide interest due to their high surface-to-volume ratio with preferential electron transport towards the Ti back-contact, and a scalable synthesis by electrochemical anodization [3]. However, thermal annealing is needed to obtain anatase and rutile phases, besides achieving suitable ratio of mixed-phases for relatively high photocatalytic performance through efficient inter-granular charge transfer and minimizing the recombination processes. Temperature induced changes in surface morphology, grain size, crystal structure and composition also have significant influence on the photo-electrochemical properties of TNTs. Here, we report the synthesis of TNTs, and the correlation of optical band gap with structural transformation from anatase to rutile through intermediate mixed phases as a function of temperature and their corresponding effect on photocatalysis application. This is confirmed by means of UV-Vis spectroscopy, X-ray diffraction (XRD) and Raman Spectroscopy. X-ray Photoelectron Spectroscopy (XPS) analyses has also been carried out to understand the change in chemical behavior with annealing temperature, gives a clear evidence of sub-stoichiometric to stoichiometric TiO2 (Ti4+) phase transformation with increasing temperature via removal of the fluorine (F) species from the NT surface which eventually changes the crystallinity of the samples as observed in XRD patterns. Further, to comprehend the change in the local coordination environment of the constituent atoms in TiO2 nanotubes with annealing temperature, the samples have been characterized by X-ray Absorption Spectroscopy (XAS). Density functional theory (DFT) has also been employed to understand the underlying mechanism.

Localization transitions and mobility edges in coupled Aubry-André chains

We study the localization transitions for coupled one-dimensional lattices with quasiperiodic potential. Besides the localized and extended phases there is an intermediate mixed phase which can be easily explained decoupling the system so as to deal with effective uncoupled Aubry-Andr\'e chains with different transition points. We clarify, therefore, the origin of such an intermediate phase finding the conditions for getting a uniquely defined mobility edge for such coupled systems. Finally we consider many coupled chains with an energy shift which compose an extension of the Aubry-Andr\'e model in two dimensions. We study the localization behavior in this case comparing the results with those obtained for a truly aperiodic two-dimensional (2D) Aubry-Andr\'e model, with quasiperiodic potentials in any directions, and for the 2D Anderson model.

Oxygen mediated phase transformation in room temperature grown TiO2 thin films with enhanced photocatalytic activity

Room temperature transformation from anatase (A-TiO2) to rutile (R-TiO2) thin films through an intermediate mixed phase on stainless steel driven by a controlled oxygen flow rate (OFR) is investigated. Such OFR dependent phase transition is confirmed by X-ray diffraction and also consistent with X-ray absorption spectroscopy at Ti L and O K-edges, showing a long range ordering in TiO6 octahedral symmetry. X-ray photoelectron spectroscopy reveals a gradual reduction in Ti2O3 and/or TiO intermediate phases with increasing OFR. Finally, an enhanced photocatalytic activity is observed in the mixed phase and discussed in terms of photo-generated charge transport in the type-II staggered band structure between A-TiO2 and R-TiO2 phases.

Monostotic Paget Disease of the Lumbar Vertebrae: A Pathological Mimicker.

Paget disease is a metabolic disorder involving abnormal bone turnover that consists of 3 phases: the initial lytic phase, the intermediate mixed phase, and the chronic sclerotic phase. Paget disease mostly presents as polyostotic or monostotic lesions of the spine, and is rare on the Indian subcontinent. We present a case of isolated Paget disease of the lumbar third vertebra, which was confirmed only at biopsy. The patient presented with chronic low backache with a developing neurological deficit. We managed the patient with posterior spinal stabilisation, using pedicular screws and vertebroplasty of the collapsed vertebrae to regain the height. Upon the diagnosis of Paget disease, the patient was treated with calcitonin and bisphosphonates for 3 months, along with regular monitoring of alkaline phosphatase levels. Through this case, we hope to emphasize that Paget disease should be considered in the differential diagnosis of lytic lesions. Additionally, the alkaline phosphatase level in this patient was high-normal, which was an aspect of the role of Paget disease as a mimicker. Confirmatory biopsy is mandatory in all lesions.

Deciphering M–T diagram of shape memory Heusler alloys: reentrance, plateau and beyond

We present our recent results on temperature behaviour of magnetization observed in Heusler alloys. Three regions can be distinguished in the M–T diagram: (I) low temperature martensitic phase (with the Curie temperature K), (II) intermediate mixed phase (with the critical temperature K) exhibiting a reentrant like behavior (between and ) and (III) high temperature austenitic phase (with the Curie temperature K) exhibiting a rather wide plateau region (between and ). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M–T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg–Landau scenario.

Radial modes of slowly rotating compact stars in the presence of magnetic field

Compact stars are composed of very high-density hadron matter. When the matter is above nuclear matter density, then there is a chance of different phases of matter such as hadron matter to quark matter. There is a possible phase which, having the quark core surrounded by a mixed phase followed by hadronic matter, may be considered as a hybrid phase inside the stars called hybrid star (HS). The star which consists of only u, d and s quarks is called quark star (QS) and the star which has only hadronic matter is called neutron star (NS). For the equation of state (EOS) of hadronic matter, we have considered the Relativistic Mean Field (RMF) theory and we incorporated the effect of strong magnetic fields. For the EOS of the quark phase we use the simple MIT bag model. We have assumed Gaussian parametrization to make the density dependent for both bag pressure in quark matter and magnetic field. We have constructed the intermediate mixed phase by using the Glendenning conjecture. Eigenfrequencies of radial pulsations of slowly rotating magnetized compact stars (NS, QS, HS) are calculated in a general relativistic formalism given by Chandrasekhar and Friedman. We have studied the effect of central density on the square of the frequencies of the compact stars in the presence of zero and strong magnetic field.

Poly(N-2-(methacryloyloxy)ethyl pyrrolidone)-poly(benzyl methacrylate) diblock copolymer nano-objects via RAFT alcoholic dispersion polymerisation in ethanol

N-2-(methacryloyloxy)ethyl pyrrolidone (NMEP) is a highly polar monomer that is much more readily copolymerised with methacrylic monomers than its structural analogue, N-vinyl pyrrolidone. The RAFT solution polymerisation of NMEP has been conducted in ethanol at 70 °C while varying the degree of polymerisation (DP) from 70 to 400. Reducing the CTA/initiator molar ratio from 10.0 to 3.0 when targeting PNMEP100 led to a three-fold rate enhancement and increased the final monomer conversion from 72% to 98%. Targeting DPs of 200 or greater led to lower monomer conversions. DMF GPC analysis of a series of PNMEPx homopolymers confirmed a linear increase in molecular weight with conversion and relatively low dispersities (Mw/Mn < 1.26). A PNMEP50 macro-CTA was chain-extended with benzyl methacrylate (BzMA) via RAFT alcoholic dispersion polymerisation. High BzMA conversions (>90%) were obtained and electron microscopy studies indicated that a range of diblock copolymer morphologies, e.g. spheres, worms and vesicles, were produced by polymerisation-induced self-assembly (PISA). Finally, a PNMEP47-PBzMA243 diblock copolymer was synthesised via a convenient ‘one-pot’ protocol whereby a PNMEP47 macro-CTA was first prepared at 97% conversion, followed by in situ RAFT dispersion polymerisation of BzMA to produce diblock copolymer nano-objects. TEM analysis of aliquots taken during the diblock copolymer synthesis indicated a gradual evolution in copolymer morphology from spherical micelles after 1 h to a pure vesicle phase after 8 h via intermediate mixed phases (including worms).

Hybrid compact star in the presence of strong magnetic field

Compact neutron stars (NSs) can consist of either hadronic matter or strange quark matter or exotic color superconducting matter. If the stars have a quark core and are surrounded by hadronic matter, they are called hybrid stars (HSs). The HS is a mixture of the hadron and exotic quark phases. Observational results suggest that magnetars are certain NSs having huge surface magnetic field. We calculate equation of states (EOSs) of hadronic and quark matter at high densities in the presence of strong magnetic field and then study the quark–hadron phase having mixed phase in between giving rise to hybrid star. The intermediate mixed phase is constructed based on the Glendenning conjecture. The magnetic field significantly affects the EOS of the matter if the field strength is above [Formula: see text]G. We also calculate HS structure parameters such as the maximum mass, radius, moment of inertia, fundamental period and surface redshift and compare them specially the maximum mass with the recent observation of pulsars PSR 1903+0327 and PSR J1614-2230. The observation restricts a severe constraint on the EOS of matter at extreme conditions.

Coexistence of magnetic order and Kondo effect in the Kondo-Heisenberg model

The Kondo lattice model is investigated through a fermionic mean-field approximation. The obtained phase diagram, including the pure ferromagnetic (FM), antiferromagnetic (AF), Kondo (K), and mixed phases, is in good agreement with previous studies. Calculations on the simple cubic and square lattices confirm a robust coexistence of ferromagnetism and Kondo effect (FM + K), sustained by a partial Kondo screening, which leads to the concept of a spin selective Kondo insulator. We have also obtained a coexistence of antiferromagnetism and Kondo effect (AF + K), which requires the intervenience of a next-nearest-neighbor hopping ${t}^{\ensuremath{'}}$ and a Heisenberg exchange ${J}_{ij}$. The effect of temperature and pressure is described by the behavior of the order parameters. The corresponding N\'eel temperature ${T}_{N}$ and Kondo temperature ${T}_{K}$ are plotted in the form of a Doniach diagram. The presence of the intermediate mixed phases is fundamental to determine the order of the magnetic phase transitions as one approaches the quantum critical point.

Radial modes of oscillations of slowly rotating magnetized compact hybrid stars

Stars having a quark core surrounded by a mixed phase followed by hadronic matter are termed as hybrid stars(HS). For the equation of state(EOS) of hadronic matter, we have considered RMF(Relativistic Mean Field) theory, in the presence of strong magnetic fields leading to Landau quantization of the charged particles. For the EOS of quark phase we have used the simple MIT bag model also in presence of strong magnetic field. The bag pressure and magnetic field are parametrized to make density dependant. We have constructed the intermediate mixed phase by using Glendenning conjecture. The EOSs are constructed comprising the hadron, mixed and quark phases. Eigenfrequencies of radial pulsations of slowly rotating magnetised hybrid star are calculated using constructed EOSs in a general relativistic formalism given by Chandrasekhar and Friedman.

Maximum mass and radial modes of hybrid star in presence of strong magnetic field

It is believed that neutron stars (NS) consist of hadronic and exotic states like strange quark or color superconducting matter. Stars having a quark core surrounded by a mixed phase followed by hadronic matter, may be considered as hybrid stars (HS). The mixed phase is well proportionate of both the hadron and quark phases. A huge magnetic field is predicted in core as well as on surface of the neutron star. Here we study the effect of this strong magnetic field on the equation of states(EOS) of HS matter. We further study the hadron-quark phase transition in the interiors of NS giving rise to HS in presence of strong magnetic field. We finally study the effect of strong magnetic field on maximum mass and eigenfrequencies of radial pulsation of such type of HS. For the EOS of hadronic matter, we have considered RMF(Relativistic Mean Field) theory and we incorporated the effect of strong magnetic fields leading to Landau quantization of the charged particles. For the EOS of quark phase we use the simple MIT bag model. We have assumed Gaussian parametrization to incorporate the density dependence of both bag pressure and magnetic field. We have constructed the intermediate mixed phase by using Glendenning conjecture. We found that magnetic field softens the EOS of both the phases, as a result the maximum mass is reduced for HS and period of oscillation is increased significantly for primary mode.

Neutron star in the presence of strong magnetic field

Compact stars such as neutron stars (NS) can have either hadronic or exotic states like strange quark or colour superconducting matter. Stars can also have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and the quark phases. Observational results suggest huge surface magnetic field in certain NS. Therefore, we study here the effect of strong magnetic field on the respective equation of states (EOS) of matter under extreme conditions. We further study the hadron–quark phase transition in the interiors of NS giving rise to HS in the presence of strong magnetic field. The hadronic matter EOS is described based on RMF theory and we include the effects of strong magnetic fields leading to Landau quantization of the charged particles. For quark phase, we use the simple Massachusetts Institute of Technology (MIT) bag model, assuming density-dependent bag pressure and magnetic field. The magnetic field strength increases from the surface to the centre of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. We finally study, the mass–radius relationship for such types of mixed HS, calculating their maximum mass, and compare them with the recent observations of pulsar PSR J1614-2230, which is about 2 solarmass.

Maximum mass of a hybrid star having a mixed-phase region based on constraints set by the pulsar PSR J1614-2230

Recent observation of pulsar PSR J1614-2230 with a mass of about two solar masses poses a severe constraint on the equations of state (EOSs) of matter describing stars under extreme conditions. Neutron stars (NSs) can reach the mass limit set by PSR J1614-2230, but stars having hyperons or quark stars (QSs) having boson condensates, with softer EOSs, can barely reach such limit and are ruled out. QSs with pure strange matter cannot attain such high mass unless the effect of strong coupling constants or color superconductivity are considered. In this work I calculate the upper mass limit for a hybrid star (HS) having a quark-hadron mixed phase. The hadronic matter (having hyperons) EOS is described by relativistic mean field theory and the quark matter EOS is modeled according to the Massachusetts Institute of Technology bag model. The intermediate mixed phase is constructed using the Glendenning prescription. A HS with a mixed phase cannot reach the mass limit set by PSR J1614-2230 unless one assumes a density-dependent bag constant. However, for such case the mixed-phase region is small. The maximum mass of a mixed hybrid star obtained with such a mixed-phase region is $2.01{M}_{\ensuremath{\bigodot}}$. A stiffer hadronic EOS can raise the maximum mass of a mixed HS to $2.1$ ${M}_{\ensuremath{\bigodot}}$.

Phase diagram of vortex matter of type-II superconductors

We propose a model to construct the phase diagram for type-II superconductors through molecular-dynamics simulation. In this model, the Abrikosov vortices interact with long-range repulsion and short-range attraction. We are able to obtain the phase diagrams consisting of the vortex lattice, the intermediate-mixed phase (IMP), and the disordered vortex phase in the $B$-$T$, $B$-$\ensuremath{\kappa}$, and $B$-$q$ planes, where $B$ is induction, $\ensuremath{\kappa}$ is the Ginzburg-Landau parameter, and $q$ is the relative strength of the attraction to repulsion interactions between vortices. The IMP is in the form of a superlattice of either vortex bubbles or parallel vortex stripes, agreeing excellently with experimental results that have not yet been explained by existing models.

Role of solute and solvent on the deposition of ZnO thin films

ZnO thin films have been deposited on SnO 2:F coated transparent conducting oxide (TCO) glass substrates, using a simple electrochemical (galvanic) technique, from different electrolytic solutions. A detailed investigation on the effect of different solute and solvent on the deposition process has been made. We have established that galvanically obtained ZnO thin films can be deposited with various morphologies depending on the nature of the solute and solvent used. ZnO formation can happen either directly or through an intermediate mixed phase following different reaction paths. Structural, morphological, compositional and optical characterizations of the films developed under different conditions were carried out to study such effects. The films were also tested for their potential use as methane sensor.

Non-Fermi-liquid phases in the two-band Hubbard model: finite-temperature exact diagonalization study of Hund's rule coupling

The two-band Hubbard model involving subbands of different widths is investigated via finite-temperature exact diagonalization (ED) and dynamical mean field theory (DMFT). In contrast to the quantum Monte Carlo (QMC) method which at low temperatures includes only Ising-like exchange interactions to avoid sign problems, ED permits a treatment of Hund's exchange and other onsite Coulomb interactions on the same footing. The role of finite-size effects caused by the limited number of bath levels in this scheme is studied by analyzing the low-frequency behavior of the subband self-energies as a function of temperature, and by comparing with numerical renormalization group (NRG) results for an effective one-band model. For half-filled, non-hybridizing bands, the metallic and insulating phases are separated by an intermediate mixed phase with an insulating narrow and a bad-metallic wide subband. The wide band in this phase exhibits different degrees of non-Fermi-liquid behavior, depending on the treatment of exchange interactions. Whereas for complete Hund's coupling, infinite lifetime is found at the Fermi level, in the absence of spin-flip and pair-exchange, this lifetime becomes finite. Excellent agreement is obtained both with new NRG and previous QMC/DMFT calculations. These results suggest that-finite temperature ED/DMFT might be a useful scheme for realistic multi-band materials.

Optical properties of silicon thin films related to LPCVD growth condition

In this paper we study the changes in the microstructural and optical properties of silicon thin films produced by the variation of the parameters (temperature and pressure) of the low-pressure chemical vapour deposition (LPCVD) process. Silicon thin films prepared by LPCVD on oxidized silicon substrates over a large range of process parameters ( T dep=500–615°C, p dep=20–100 Pa) have been characterized by Raman spectroscopy, spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. The phase transition of as-deposited silicon from an amorphous to a crystalline phase via an intermediate mixed phase (few grains in amorphous silicon matrix) can be monitored by the changes in the optical properties and in the Raman spectra. LPCVD parameters, which control the deposition kinetics, are able to influence the optical properties, the structure and/or morphology of the as-deposited LPCVD silicon films. The SE and Raman results prove that it is possible to grow by LPCVD (from pure silane), a silicon film in a (poly)crystalline state at a temperature as low as 500°C.

The magnetic structure of Tb-Tm alloys studied by neutron diffraction

Single crystals of Tb-Tm alloys with Tm contents of 12%, 40%, 55% and 65% were investigated by neutron diffractometry over the temperature range 4.2-300K. All these alloys order magnetically to a basal plane spiral below the Neel temperature. Below the Curie temperature the magnetic ordering of the Tb-12% Tm alloy is ferromagnetic with the moments in the basal plane, while the other alloys have a ferromagnetic component along the c axis and a spiral component in the basal plane below Tc. The Tb-55%Tm and the Tb-65%Tm alloys have an intermediate mixed phase, where the c axis component is modulated along the c axis (CAM structure). Tb-Tm alloys have an inhomogeneous phase, where the spins associated with the Tb ions lie in the basal plane, while the spins associated with the Tm ions order along the c axis.