Modern Physics Letters B

Periodicity (in time or space) is a part and parcel of every living being: one can see, hear and feel it. Everyday examples are locomotion, respiration and heart beat. The reinforced N-dimensional periodicity over two or more crystalline solids results in the so-called phononic band gap crystals. These can have dramatic consequences on the propagation of phonons, vibrations and sound. The fundamental physics of cleverly fabricated phononic crystals can offer a systematic route to realize the Anderson localization of sound and vibrations. As to the applications, the phononic crystals are envisaged to find ways in the architecture, acoustic waveguides, designing transducers, elastic/acoustic filters, noise control, ultrasonics, medical imaging and acoustic cloaking, to mention a few. This review focuses on the brief sketch of the progress made in the field that seems to have prospered even more than was originally imagined in the early nineties.

We construct a one-dimensional (1D) theoretical model to clarify the occurrence of superconductivity. The weak-coupling (WC) theory allows a determination of the phase diagram. The constrained hopping induces additional two-body and three-body interactions. At half-filling, the three-body interaction is responsible for the triplet superconducting (TS) correlation. Away from half-filling, the two-body interaction works, favoring the singlet superconducting (SS) correlation. The results are expected to provide an insignificant insight into the superconductivity mechanism.

We investigate theoretically and numerically the tunable plasmon-induced transparency (PIT) phenomenon in graphene-sheet system in infrared range. We show that when surface plasmon polaritons (SPPs) propagate along a monolayer graphene sheet with two detuned side-coupled resonators, the PIT-like transmission spectra of SPPs appear. Thanks to the tunable permittivity of graphene by bias voltages, the resonant wavelength of side-coupled resonators can be changed. So the transmission spectra can be tuned dynamically and the tunable PIT phenomenon is achieved. Numerical simulation by finite element method is conducted to verify our design.

In this research, single phase $\alpha$-MoSi₂ was prepared by solid state hybrid microwave heating within 90 min at relatively low temperature 1273 K. Such precursor powders were then ball milled and sintered by microwave heating at different temperatures. The thermoelectric (TE) properties of MoSi₂ bulks were investigated in the temperature range of 300–673 K. When the sintering temperature increases from 973 K to 1273 K, the electrical resistivity decreases significantly and the Seebeck coefficients increase obviously, leading to the maximum TE powder factor of $6.2\times 10^{-6}{\mathrm{\text{Wm}}}^{-1}{\mathrm{\text{K}}}^{-2}$ at 673 K. These results demonstrate the feasibility of high efficient and economical synthesis of MoSi₂ by microwave heating technique, with the final products having comparable TE performance in comparison to those from typical methods with long duration and energy-extensive consumption.

The current commercially, available Bonner sphere neutron spectrometer (BSS) has high sensitivity to neutrons below 20 MeV, which causes it to be poorly placed to measure neutrons ranging from a few MeV to 100 MeV. The paper added moderator layers and the auxiliary material layer upon ³He proportional counters with FLUKA code, with a view to improve. The results showed that the responsive peaks to neutrons below 20 MeV gradually shift to higher energy region and decrease slightly with the increasing moderator thickness. On the contrary, the response for neutrons above 20 MeV was always very low until we embed auxiliary materials such as copper (Cu), lead (Pb), tungsten (W) into moderator layers. This paper chose the most suitable auxiliary material Pb to design a three-tier architecture multi-sphere neutron spectrometer (NBSS). Through calculating and comparing, the NBSS was advantageous in terms of response for 5–100 MeV and the highest response was 35.2 times the response of polyethylene (PE) ball with the same PE thickness.

Chaos control of a Bose–Einstein condensate (BEC) loaded into a moving optical lattice with attractive interaction is investigated on the basis of Lyapunov stability theory. Three methods are designed to control chaos in BEC. As a controller, a bias constant, periodic force, or wavelet function feedback is added to the BEC system. Numerical simulations reveal that chaotic behavior can be well controlled to achieve periodicity by regulating control parameters. Different periodic orbits are available for different control parameters only if the maximal Lyapunov exponent of the system is negative. The abundant effect of chaotic control is also demonstrated numerically. Chaos control can be realized effectively by using our proposed control strategies.

In virtue of the particle swarm optimization (PSO) algorithm, the global minimum candidate structures with the lowest energy for ${({\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4)}_n(n=1-3)$ clusters were obtained by first-principles structural searches. The geometric structures and spin configurations of three cationic ${({\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4)}_n^{+}(n=1-3)$ clusters have been identified for the first time by comparing the experimental IR spectra with the calculated results from density functional theory by using different exchange-correlation functionals. It is found that the lowest energy structures of these clusters are of a shape of hat, boat and tower, respectively, with a ferrimagnetic arrangement of spins, and M06L functional is more suitable for ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ clusters than other ones.

In this paper, the equilibrium properties of spin-1 Blume–Capel model are studied by using constant-coupling approximation. The formulation is based on developed by Obokata and Oguchi method, where the dependence upon the thermodynamic variables is determined by a set of two-couple nonlinear algebraic equations. The temperature dependence of the order parameters is examined to characterize the nature (continuous or discontinuous) of the phase transitions and to obtain the metastable and unstable branches. For the system, the effect of the uniaxial anisotropy parameter to phase transitions and stable, metastable and unstable states is discussed on the simple cubic lattice with the coordination number $z$ = 6.

CaWO₄ crystals were prepared by hydrothermal method assisting with phenol-formaldehyde polymer. The morphology can be controlled by polymer, and X-ray diffraction patterns results present a scheelite-type tetragonal structure, characteristic infrared active modes for O–W–O in the range from 500 cm${}^{-1}$ to 4000 cm${}^{-1}$ by Fourier transform infrared spectroscopic techniques. Raman results indicate that the crystals possess seven Raman active modes in the range from 100 cm${}^{-1}$ to 1000 cm${}^{-1}$. A scanning electron microscopy study reveals that the particles exhibit uniform morphology. Luminescent properties were investigated by photoluminescence measurements, multicolor phosphors were obtained when Ca${}^{2+}$ was substituted partly by lanthanide ions.

Previously, we reported that the $d$–$p$ (Mn-$3d$–O-$2p$) orbital hybridization induces Mn valence change (Mn${}^{3+}\to$Mn${}^{4+}$) in the octahedron. The electron transfer mechanism can be controlled by modifying the Mn-$3d$ orbital in the octahedron. Here, we used the density functional theory (DFT) with generalized gradient approximation (GGA) and two-dimensional correlation analysis (2D-CA) techniques to calculate the electron transfer mechanism of the V (Nb or Ta) substituted NiMn₂O₄ (NMO) in the temperature range of 50–1500 K. The results show that the heat accumulation accelerates the O-$2p^4$ orbital splitting, inducing charge disproportionation. The V-$3d^3$ substituted Mn increases the intensity and of the partial density of state (PDOS) at conduction band (1–3 eV), this enhances the V-$3d^3$–O-$2p^4$ $p$–$d$ ${\sigma }^{\ast }$ orbital. The Nb-$4d^3$/Ta-$5d^3$ substituted Mn reduces the intensity of the PDOS at conduction band (1–5 eV), this weakens the Nb-$4d^3$/Ta-$5d^3$–O-$2p^4$ $p$–$d$ ${\sigma }^{\ast }$ orbital. This study effectively analyzes the microscopic changes of the electron transfer caused by the heat accumulation, provides a theoretical basis for the design of NMO-based negative temperature coefficient (NTC) thermistors.

The geometrical, electronic and magnetic properties of the Zn${}_{0.75}$Mo${}_{0.25}$M (M=S, Se and Te) have been studied by spin-polarized first-principles calculation. The optimized lattice constants of 5.535, 5.836 and 6.274 Å for M=S, Se and Te are related to the atomic radius of 1.09, 1.22 and 1.42 Å for S, Se and Te atoms, respectively. The Zn${}_{0.75}$Mo${}_{0.25}$M are magnetic half-metallic (HM) with the spin-down conventional band gaps of 2.899, 2.126 and 1.840 eV, while the HM band gaps of 0.393, 0.016 and 0.294 eV for M=S, Se and Te, respectively. At the Fermi level, the less than half-filled Mo-$4d$ orbital hybridizated with the less M-$p$ orbital contributes only spin-up channel leading Zn${}_{0.75}$Mo${}_{0.25}$M an HM ferromagnetism. The tetrahedral crystal field formed by adjacent three Zn atoms and one M atom splits the spin-up channel (majority spin) of Mo-$4d$ orbital into three-fold degenerate $t_{2g}(d_{xy},d_{yz},d_{zx})$ states at the Fermi level and double degenerate $e_g$ $(d_{z^2},d_{x^2-y^2})$ states below the Fermi level. The exchange splitting energies of the Zn${}_{0.75}$Mo${}_{0.25}$M are −2.611, −2.231 and −1.717 eV for M=S, Se and Te, respectively. The results provide an useful theoretical guidance for Zn${}_{0.75}$Mo${}_{0.25}$M applications in spintronic devices.

In this work, we performed differential scanning calorimetry (DSC) experiments to investigate the phase transition temperature and the molar enthalpy of the absorbed water confined in porous titanium dioxide. The porous titanium dioxide with three different pore size distribution and different filling fraction of the absorbed water were examined. We found that both the pore size of the examined samples and the filling fraction of the absorbed water affected the water’s phase transition temperature and its molar enthalpy.

The integrability of a super generalized Hirota equation (GHE) is investigated by means of the fermionic covariant prolongation structure theory. We construct the $\mathrm{\text{su}}(2/1)\times R(\lambda )$ prolongation structure for the super GHE and derive the corresponding Lax representation and the Bäcklund transformation. In addition, a solution of the super integrable equation is presented.

Barium hexaferrite nanoparticles are attractive for modern data storage and microwave devices due to their unique properties. Single phase synthesis of barium hexaferrite using sol–gel auto-combustion route was optimized by varying sintering temperature and time. X-ray diffraction confirmed single phase hexagonal crystal structure of the sample sintered at 1100${}^{\circ }$C for 2 h. Crystallite size, as determined using Scherrer’s formula, was increased with the increase in sintering temperature while the porosity remained nearly unchanged. Field emission scanning electron microscope (FE-SEM) revealed that grain size was increased from nanometers to micrometers by rising the sintering temperature and the shape of particles was platelet-like hexagonal at 900${}^{\circ }$C. Vibrating sample magnetometer (VSM) exhibited that saturation magnetization and coercivity increased with the increase of sintering temperature. Maximum saturation magnetization and coercivity values were 36.80 emu/g and 5365 Oe, respectively, for the sample sintered at 1100${}^{\circ }$C for 2 h.

Selective laser melting (SLM)-fabricated AlSi10Mg parts were heat-treated under vacuum to eliminate the residual stress. Microstructure evolutions and tensile properties of the SLM-fabricated parts before and after vacuum annealing treatment were studied. The results show that the crystalline structure of SLM-fabricated AlSi10Mg part was not modified after the vacuum annealing treatment. Additionally, the grain refinement had occurred after the vacuum annealing treatment. Moreover, with increasing of the vacuum annealing time, the second phase increased and transformed to spheroidization and coarsening. The SLM-produced parts after vacuum annealing at 300${}^{\circ }$C for 2 h had the maximum ultimate tensile strength (UTS), yield strength (YS) and elongation, while the elastic modulus decreased significantly. In addition, the tensile residual stress was found in the as-fabricated AlSi10Mg samples by the microindentation method.