Reversible and irreversible domain wall dynamics in [011]C oriented relaxor ferroelectric single crystals

Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]_C-oriented 0.27Pb(In_1/2Nb_1/2)O₃-0.46Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Q_m and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor-doped single crystals and mainly guides on further performance optimization in PbTiO₃-based relaxor single crystals.     

Effect of annealing temperature on microstructure and thermoelectric transport properties of Cu2.1Zn0.9SnSe4 alloys

Cu-based quaternary chalcogenide compounds have been thermoelectric topic of interest among researchers, especially in recent years, due to their intrinsically low thermal conductivity. Recently plenty of work is done on thermoelectric properties of Cu₂ZnSnSe₄-based alloys emphasizing on importance of Cu₂ZnSnSe₄-based alloys in thermoelectric power generation. In this study, we report the effect of annealing temperature on microstructure and thermoelectric properties of Cu_2.1Zn_0.9SnSe₄ alloys. Cu_2.1Zn_0.9SnSe₄ compounds were synthesized by high-temperature melting followed by annealing at four different temperatures (600 °C, 650 °C, 700 °C and 725 °C). X-ray diffraction combined with Raman spectroscopy confirmed the presence of Cu₂ZnSnSe₄ phase along with ZnSe and CuSe secondary phases. The increased annealing temperature critically affected the microstructure of Cu_2.1Zn_0.9SnSe4 alloys. Successive increase in annealing temperature subsequently increases the average grain size from 7.3 for 600 sample to 12.1 μm for 725 °C sample by shifting grain size distribution toward higher range. Increased grain size results in reduced carrier scattering and decreases the electrical resistivity eventually improving power factor and maximum power factor of about 400 μWk^?2 m^?1 is obtained for 725 °C sample. Besides, the increased annealing temperature resulted in increased thermal conductivity attributing increased grain size resulting in low phonon scattering. 725 °C sample shows highest power factor and moderate thermal conductivity among all the samples which resulted in highest value of figure of merit for 725 °C sample of about 0.1 at 673 K.

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Efficient MOF- derived V–Ni3S2 nanosheet arrays for electrocatalytic overall water splitting in alkali

The synergistic achievement of low-cost earth-abundant electrocatalysts and high efficiency to meet renewable energy need is highly desirable yet challenging. Here, we developed a simple Ni foam self -templating route for V-doped Ni₃S₂ nanosheet arrays through in situ formation of metal-organic frameworks (MOFs) combined with subsequent conversion. The as-prepared MOF-V-Ni₃S₂/NF catalyst delivers outstanding electrocatalytic performance in the alkaline solution, which requires low overpotentials of 118.1 mV @10 mA cm^?2 and 268 mV @10 mA cm^?2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. The V-doping and MOF-derived 3D hieratical nanostructure play a vital role in the catalytic process, which provides efficient active sites and large surface areas. Furthermore, an alkaline electrolyzer was assembled with two pieces of MOF-V-Ni₃S₂/NF, which achieves efficient water splitting at 1.58 V @10 mA cm^?2. This strategy opens up new channels to synthesize MOF-based bifunctional electrocatalysts toward overall water spitting.     

An innovative process for synthesis of superfine nanostructured Li2TiO3 tritium breeder ceramic pebbles via TBOT hydrolysis – solvothermal method

In this paper, a method combining hydrolysis of tetrabutyl orthotitanate (TBOT) and solvothermal reaction was first used to fabricate nanostructured Li₂TiO₃ tritium breeder ceramic pebbles. Initially, superfine nanostructured Li₂TiO₃ powders were synthesized with average particle size of about 10?nm, according to TEM. The surface area of precursor particles synthesized via this method was found to be 115.85?m²/g by BET analysis, which is much larger than that of the product obtained using traditional methods. The results showed that precursor particles had high sintering activity. XRD pattern revealed that the phase transition temperature for monoclinic phase Li₂TiO₃ prepared by this method was nearly 450?°C, which was the lowest phase transition temperature reported among all wet chemical methods to date. Subsequently, investigation of ceramic sintering demonstrated that Li₂TiO₃ ceramic pebbles with desired nano-crystalline sizes (27.98 ~ 55.03?nm) were obtained by sintering at 500 ~ 600?°C for 4?h. The possible mechanisms were proposed based on the reaction processes of TBOT hydrolysis, solvothermal reaction and sintering.     

An effective approach for reliability-based robust design optimization of uncertain powertrain mounting systems involving imprecise information

The uncertain parameters of automotive powertrain mounting systems (PMSs) may involve imprecise information (e.g., incomplete, different and conflicting information) in engineering practice. An effective approach is proposed for the reliability-based robust design optimization (RBRDO) of uncertain PMSs involving imprecise information. In the proposed approach, the imprecise information of uncertain parameters is firstly addressed and combined based on evidence theory, and the uncertain parameters are treated as evidence variables. Then, an uncertainty analysis method named evidence perturbation-central difference method (EPCDM) is derived to fast estimate the mean intervals, standard deviation intervals, and the belief and plausibility measures related to system inherent characteristics. A reference method named evidence-Monte Carlo method (EMCM) is developed to verify the effectiveness of EPCDM. Next, to conduct robustness design, the weighted sum of the lower bounds of means and the upper bounds of standard deviations of system inherent characteristics are taken to construct optimization objective; while to perform reliability design, the belief measures related to system inherent characteristics are used to create reliability constraints. Afterwards, a nested RBRDO model is established to explore the optimum design of the PMS, which considers both reliability and robustness simultaneously. The nested PBRDO can be effectively simplified based on EPCDM. The effectiveness of the proposed approach is finally demonstrated by the application example.

     

Structure and Properties of Nonstoichiometric Y1-xNbxO1.5+x for Thermal Barrier Coatings

Understanding the effect of nonstoichiometry on material properties is of critical importance for the Thermal Barrier Coatings (TBCs) application. In this work, the effect of nonstoichiometry was systematically investigated in Y₃NbO₇, a recently identified promising TBCs material for next-generation gas turbine engines. The results show that the nonstoichiometry effect mediates the microstructure, mechanical properties, thermophysical properties, oxygen ionic conductivity and optical transmittance. The results suggest that the oxygen ionic conductivity is correlated to the mass diffusion in the oxygen-deficient fluorite oxides Y_1-xNb_xO_1.5+x. The stoichiometric composition Y₃NbO₇, with the lowest thermal conductivity and slowest mass diffusion in Y_1-xNb_xO_1.5+x series, is optimal for the TBCs application, which can be of relevance for TBCs material design and coating fabrication.