Strong electron correlation-induced Mott-insulating electrides of Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)

The presence of interstitial electrons in electrides endows them with interesting attributes,such as low work function,high carrier concentration,and unique magnetic properties.Thorough knowledge and understanding of electrides are thus of both scientific and technological significance.Here,we employ first-principles calculations to investigate Mott-insulating Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)electrides with Mn_(5)Si_(3)-type structure,in which half-filled interstitial electrons serve as ions and are spin-polarized.The Mott-insulating property is induced by strong electron correlation between the nearest interstitial electrons,resulting in spin splitting and a separation between occupied and unoccupied states.The half-filled antiferromagnetic configuration and localization of the interstitial electrons are critical for the Mott-insulating properties of these materials.Compared with that in intermetallic electrides,the orbital hybridization between the half-filled interstitial electrons and the surrounding atoms is weak,leading to highly localized magnetic centers and pronounced correlation effects.Therefore,the Mott-insulating electrides Ae_(5)X_(3)have very large indirect bandgaps(0.30 eV).In addition,high pressure is found to strengthen the strong correlation effects and enlarge the bandgap.The present results provide a deeper understanding of the formation mechanism of Mott-insulating electrides and provide guidance for the search for new strongly correlated electrides.

Reaction mechanism of metal and pyrite under high-pressure and high-temperature conditions and improvement of the properties

Pyrite tailings are the main cause of acid mine wastewater.We propose an idea to more effectively use pyrite,and it is modified by exploiting the reducibility of metal represented by Al under high-pressure and high-temperature(HPHT)conditions.Upon increasing the Al addition,the conductivity of pyrite is effectively improved,which is nearly 734 times higher than that of unmodified pyrite at room temperature.First-principles calculations are used to determine the influence of a high pressure on the pyrite lattice.The high pressure increases the thermal stability of pyrite,reduces pyrite to highconductivity Fe7S8(pyrrhotite)by Al.Through hardness and density tests the influence of Al addition on the hardness and toughness of samples is explored.Finally we discuss the possibility of using other metal-reducing agents to improve the properties of pyrite.

Utilizing of high-pressure high-temperature synthesis to enhance the thermoelectric properties of Zn_(0.98)Al_(0.02)O with excellent electrical properties

The temperature in the high-pressure high-temperature(HPHT) synthesis is optimized to enhance the thermoelectric properties of high-density Zn O ceramic, Zn_(0.98)Al_(0.02)O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that HPHT can be utilized to control the crystal structure and relative density of the material.High pressure can be utilized to change the energy band structure of the samples via changing the lattice constant of samples, which decreases the thermal conductivity due to the formation of a multi-scale hierarchical structure and defects. The electrical conductivity of the material reaches 6×10^(4) S/m at 373 K, and all doped samples behave as n-type semiconductors. The highest power factor(6.42 μW·cm^(-1)·K^(-2)) and dimensionless figure of merit(z T = 0.09) are obtained when Zn_(0.98)Al_(0.02)O is produced at 973 K using HPHT, which is superior to previously reported power factors for similar materials at the same temperature. Hall measurements indicate a high carrier concentration, which is the reason for the enhanced electrical performance.

Properties of B4C-TiB2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.

Parametric study on controllable growth of SrZrS_(3)thin films with good conductivity for photodetectors

SrZrS_(3)is a promising chalcogenide perovskite with unique advantages including high abundance of consisting elements,high chemical stability,strong light absorption above its direct band gap,excellent carrier transport ability.While unfortunately,due to the lack of breakthroughs in its thin film synthesis technique,its optoelectronic properties are not fully investigated,not to mention the device applications.In this work,large-area and uniform SrZrS_(3)thin film(5 cm×5 cm)was prepared by facile sputtering method,followed by a post-annealing treatment at a high temperature of 1000℃for 2–12 h under CS_(2)atmosphere.All SrZrS_(3)samples prepared adopt distorted orthorhombic structure with pnma space group and have high crystallinity.In addition,the band gap of SrZrS_(3)thin film is measured to be 2.29 eV,higher than that of the powder form(2.06 eV).Importantly,the light absorption coefficient of SrZrS_(3)thin film reaches over 105 cm^(−1),the carrier mobility is as high as 106 cm^(2)/(V∙s).The above advantages allow us to use the SrZrS_(3)thin film as photoactive layer for photodetector applications.Finally,a symmetrically structured photoconductive detector was fabricated,performing a high responsivity of 8 A/W(405 nm light excitation).These inspiring results promise the glorious application potential of SrZrS_(3)thin film in photodetectors,solar cells,other optoelectronic devices.

High-thermoelectric performance of TiO_(2-x)fabricated under high pressure at high temperatures

We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy,combining high pressure and high temperature(HPHT)reactive sintering with appropriate ratio of coarse Ti to nanosized TiO_(2).Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT.The thermoelectric performance was significantly enhanced,and rather low thermal conductivity(1.60 W m^(-1)K^(-1))for titanium oxide was reported here for TiO1.76.Correspondingly,a high dimensionless figure of merit(zT)up to 0.33 at 700℃was realized in it.As far as we know,this value is an enhancement of 43%of the ever best result about nonstoichiometric TiO_(2)and the result is also exciting for oxide thermoelectric materials.The moderate power factor,the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance.We develop a facile strategy for preparing multi-scale hierarchical TiO_(2-x)and its superior ability to optimize thermoelectric performance has been demonstrated here.

Pressure-induced photoluminescence enhancement and ambient retention in confined carbon dots

Piezochromic luminescent materials have shown great potential in advanced optoelectronic applications.However,most of luminescent materials usually undergo emission quenching under external stimuli.Herein,we demonstrate for the first time that the photoluminescence of carbon dots(CDs)confined within sodium hydroxide can be enhanced when high pressure is applied.They exhibit a 1.6-fold fluorescence enhancement compared with pristine CDs.Importantly,the enhanced fluorescence intensity can be retained after the release of pressure to ambient conditions.A combination of experimental analysis and theoretical simulations indicates that such an enhanced emission is mainly attributed to the strong confinement resulting from the sodium hydroxide matrix,which can separate the CDs spatially and restrict the nonradiative pathway.These results provide a rational strategy for manipulating the optical properties of CDs with enhanced and retainable photoluminescence(PL)performance,thus opening up a venue for designing luminescent CDs-based materials.

BDNF基因rs6265多态性与父母严厉管教对学前儿童工作记忆的交互影响

工作记忆是执行功能的重要组成部分,基因与家庭环境因素如何交互影响学前儿童工作记忆,目前尚缺少研究.本研究以632名学前儿童(平均年龄=5.14岁,SD=0.94)为被试,考察了BDNF基因rs6265多态性与父母严厉管教对学前儿童工作记忆的交互影响.研究结果显示,BDNF基因rs6265多态性与父母严厉管教对学前儿童工作记忆成绩的交互作用显著.具体而言,携带Val/Val基因型学前儿童的工作记忆成绩在高父母严厉管教条件下显著降低;对于携带Met等位基因的学前儿童,其工作记忆成绩在不同父母严厉管教条件下没有显著差异.研究结果支持了素质-压力模型,表明对工作记忆发展关键期的学前儿童而言,Val/Val基因型是消极环境的脆弱性因子,携带Val/Val基因型学前儿童的工作记忆容易受到消极环境的负面影响,这为理解学前儿童工作记忆发展的基因与环境交互作用机制提供了新的证据.

Se-alloying reducing lattice thermal conductivity of Ge_(0.95)Bi_(0.05)Te

High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics.Recently,the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering.In this study,we systematically studied thermoelectric properties of Se-alloyed Ge_(0.95) Bi_(0.05) Te via theoretical calculations,structural characterizations,and performance evaluations.Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge_(0.95) Bi_(0.05) Te matrix.Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge_(0.95) Bi_(0.05) Te matrix,which can strengthen Umklapp phonon scattering.Finally,a decreased lattice thermal conductivity from∼1.02 W m^(−1) K^(−1) to∼0.65 W m^(−1) K^(−1) at 723 K is obtained in Ge_(0.95) Bi_(0.05) Te_(1-x) Se_(x) pellets with increasing the Se content from 0 to 0.3.A peak figure of merit of∼1.6 at 723 K is achieved in Ge_(0.95) Bi_(0.05) Te_(0.7) Se_(0.3) pellet,which is∼77%higher than that of pristine GeTe.This study extends the understanding on the thermoelectric performance of GeTe.

Thermoelectric performance of Cu_(2)Se bulk materials by hightemperature and high-pressure synthesis

Polycrystalline Cu_(2)Se bulk materials were synthesized by high-pressure and high-temperature(HPHT)technique.The effects of synthetic temperature and pressure on the thermoelectric properties of Cu_(2)Se materials were investigated.The results indicate that both synthetic temperature and pressure determine the microstructure and thermoelectric performance of Cu2Se compounds.The increase of synthetic temperature can effectively enhance the electrical conductivity and decrease the lattice thermal conductivity.A two-fold improvement in the power factor is obtained at synthetic temperature of 1000℃ compared to that obtained at room temperature.All b-Cu2Se samples exhibit low and temperatureindependent lattice thermal conductivity ranging from 0.3 to 0.5 Wm^(-1)K^(-1) due to the intrinsic superionic feature and the abundant lattice defects produced at high pressure.A maximum zT of 1.19 at 723 K was obtained for the sample synthesized at 3 GPa and 1000℃.These findings indicate that HPHT technology is an efficient approach to synthesize Cu_(2)Se-based bulk materials.