BSYPTx压电陶瓷的结构与压电性能研究

采用传统固相反应法,制备了(1-x)(0.96BiScO3-0.04BiYbO3)-xPbTiO3(0.58≤x≤0.66,BSYPTx)压电陶瓷.XRD图谱分析表明,BSYPTx具有钙钛矿结构,BSYPTx陶瓷四方相到三方相的转变区域存在于x=0.64附近,即是该体系的准同型相界(MPB).在相界附近, BSYPTx陶瓷具有较优良的压电性能:压电常数d33≈426 pC/N,机电耦合系数kp=0.52;介温曲线显示,BSYPTx陶瓷相界附近的居里温度TC=430 ℃.Yb3+的引入提高了BSPT陶瓷的电滞回线的矩形度,最大的剩余极化强度Pr=43 μC/cm2.     

BiYbO3掺杂对KNN LS压电陶瓷微结构与电性能的影响

采用传统陶瓷烧结工艺,制备了BiYbO3掺杂的xBiYbO3-0.95(K05Na0.5)NbO3-0.05LiSbO3(xBY-KNN-LS)(x=0～0.002,摩尔分数)无铅压电陶瓷.研究了BiYbO3掺杂对陶瓷相结构、显微组织和电性能的影响.结果表明,随着BiYbO3掺杂含量的增加,晶粒变细,居里点逐步向低温方向移动,压电性能先增加后降低,介电损耗tan δ先增加后减小.在0≤x≤0.001 5的范围内,存在斜方相与四方相共存的准同型相界,当x=0.1％时得到最佳电性能:压电常数d33=245 pC/N,机电耦合系数kp=44.75％,居里温度Tc =365℃,tan δ=4.5％.     

LiF/Li2CO3对PZT陶瓷低温烧结及压电性能的影响

采用固相合成法制备了Pb(Zr0.52Ti0.48)O3+x%LiF（PZT+x%LiF）及Pb(Zr0.52Ti0.48)O3+y%Li2CO3(PZT+y%Li2CO3)(x、y为质量分数)压电陶瓷,研究了x、y不同对PZT压电陶瓷烧结性、晶体结构、微观形貌及压电性能的影响。随着x、y的增加,PZT压电陶瓷的四方相晶胞比（c/a）均下降,但在x=y时, 与PZT+y%Li2CO3相比,PZT+x%LiF的c/a较小,居里温度基本不变,PZT+x%LiF及PZT+y%Li2CO3的压电性能小幅提升后下降,且在x=y=0.2时,其压电性能均取得最佳。结果表明,掺杂LiF、Li2CO3均能促进低温烧结,提高致密度;在1 100 ℃烧结温度下,PZT+y%Li2CO3样品性能较优,且低温烧结效果更好。但在掺杂量较大时,LiF对性能的恶化较小。     

BF-PT-BZT三元系高温压电陶瓷的介电压电温度稳定性

采用传统固相反应法制备0.54BiFeO₃-0.33PbTiO₃-0.13Ba(Zr_xTi_1-x)O₃(BF-0.33PT-0.13Ba(Zr_xTi_1-x),0.4≤x≤0.8)三元系压电陶瓷,研究了Zr含量(x)对陶瓷的微观结构以及介电、铁电和压电性能的影响。X线衍射(XRD)结果表明,BF-0.33PT-0.13Ba(Zr_xTi_1-x)三元系陶瓷为单一钙钛矿结构,当0.4≤x≤0.7时,陶瓷相结构为三方-四方相共存;当x=0.8时,陶瓷为三方相结构。扫描电子显微镜(SEM)结果表明,随着Zr含量的增加,陶瓷晶粒尺寸逐渐增加。在25～400℃时,陶瓷的压电常数d₃₃的波动小于±6%。当x=0.7时,BF-0.33PT-0.13Ba(Zr_xTi_1-x)具有最优异的综合性能,其介电常数ε_r、居里温度T     

Sb含量对0.96(K_(0.5)Na_(0.5))(Nb_(1–x)Sb_x)O_3-0.04Bi_(0.5)Na_(0.5)ZrO_3无铅压电陶瓷结构与电性能的影响

采用传统固相法制备了0.96(K_(0.5)Na_(0.5))(Nb_(1–x)Sb_x)O_3-0.04Bi_(0.5)Na_(0.5)ZrO_3(0.96KNNS_x-0.04BNZ,x=0,0.01,0.02,0.03,0.04,0.05)无铅压电陶瓷,系统研究了Sb含量对0.96KNNS_x-0.04BNZ压电陶瓷晶相组成、显微结构及压电性能的影响规律。X射线衍射分析结果表明:0.96KNNS_x-0.04BNZ陶瓷具有纯钙钛矿结构,随着Sb含量x的增加,陶瓷从正交-四方两相共存转变为四方相,x≤0.02时在正交-四方两相共存的多型相转变(Polymorphic Phase Transition,PPT)区域。在该PPT区域靠近四方相的边界x=0.02处,陶瓷具有优异的压电性能:压电常数d_(33)=354 p C/N;平面机电耦合系数k_p=43.6%;机械品质因数Q_m=46;相对介电常数ε_r=2100;介电损耗tanδ=2.6%,居里温度t_C=290℃。     

KNN-BT-BZ-CT基无铅压电陶瓷的性能研究

采用两步烧结法制备了(0.91-x)K_(0.5)Na_(0.5)NbO_3-0.03BaTiO_3-0.06BaZrO_3-xCaTiO_3[KNN-BT-BZCT]基无铅压电陶瓷,探究了在不同CaTiO_3(CT)含量下,KNN基压电陶瓷相结构变化以及对压电性能的影响。结果表明,x<0.02时,陶瓷物相出现菱方-正交双相共存。随着CT含量的增加,陶瓷晶粒尺寸先减小后增大,且其居里温度(TC)和四方-正交(TO-T)转变温度随之逐渐降低。当x=0.01时,在室温下陶瓷出现菱方-正交准同型相界,其压电常数d33=224pC/N和机电耦合系数kp=40.2%分别达到了最佳。因此,KNN基压电陶瓷中掺入BCZT可以较好地提高其压电性能。     

Sb改性CaBi_2Nb_2O_9高温压电陶瓷的研究

采用固相反应法获得改性的xSb-CaBi2Nb2O9(CBNO)(x=0~0.08)铋层状压电陶瓷。测试结果表明,加入Sb5+降低了烧结温度,提高了致密度和平面机电耦合系数,样品均为单一相,在Sb含量摩尔分数为4%时,晶粒形貌均匀,压电和机电性能达到最高,d33为12.6 pC/N,Kp=12.1%,tanδ=0.4%。添加物并没有显著降低CBNO陶瓷的居里温度,在700℃以下表现了良好的温度稳定性。     

ZnO掺杂对PNN-PZT陶瓷结构及压电性能的影响

通过传统的固相烧结法制备了Pb(Ni_(1/3)Nb_(2/3))_(0.5)(ZraTib)_(0.5)O_3+x%ZnO(PNN-PZT+x%ZnO,质量分数x=0.2,0.4,0.6,0.8)压电陶瓷,该文研究了不同ZnO含量对PNN-PZT压电陶瓷的微观形貌、相结构及压电性能的影响。通过X线(XRD)表明,过量的ZnO加入使压电陶瓷出现焦绿石相;通过扫描电镜(SEM)分析表明,当x>0.4时,ZnO的加入由于烧结温度的降低,晶界不明显。实验表明,烧结温度为1 190℃保温2h,ZnO的掺杂量x=0.4时,压电材料的综合性能最好:介电常数εr=5 596,介电损耗tanδ=2.12%,压电常数d33=534pC/N,机械耦合系数kp=0.53。     

复合离子(NaCe)取代SrBi4Ti4O15陶瓷的介电、铁电、压电特性研究

利用普通陶瓷工艺制备了A位复合离子(NaCe)取代的Sr_(1-)_x(NaCe)_x_(/2)Bi_4Ti_4O_(15)(x=0.00～0.20)压电陶瓷,研究了(NaCe)对SrBi_4Ti_4O_(15)(SBT)陶瓷的介电、铁电和压电特性的影响。研究表明,复合离子(NaCe)的取代降低了SBT陶瓷的介电损耗tanδ,降低了SBT陶瓷的矫顽电场E_c,提高了SBT陶瓷的压电系数d_(33)。纯的SBT压电陶瓷的矫顽场E_c=94 kV/cm,复合离子(NaCe)取代的SBT-NaCe(x=0.10)陶瓷的矫顽场E_c=70 kV/cm。随着复合离子(NaCe)含量的增加,SBT的压电性能先增加,然后减小。在x=0.10组分处,SBT-NaCe(x=0.10)陶瓷具有最大的压电系数d_(33)=28 pC/N,约为纯的SBT陶瓷压电系数(d_(33)约15 pC/N)的两倍,其居里温度T_C为510℃。复合离子(NaCe)取代SBT陶瓷压电性能的提高归因于复合离子(NaCe)的取代降低了SBT压电陶瓷的矫顽电场,使得SBT压电陶瓷更容易极化,从而发挥其潜在的压电性能。同时,压电性能的提高还归因于复合离子(NaCe)的取代降低了SBT压电陶瓷的介电损耗和漏电流。材料的退火实验表明:复合离子(NaCe)取代的SrBi_4Ti_4O_(15)压电陶瓷在400℃以下具有较好的压电性能温度稳定性。     

BiFeO_3改性Bi_(1/2)Na_(1/2)TiO_3-BaTiO_3基陶瓷电性能

采用固相反应法制备了新型(0.95–x)Bi1/2Na1/2TiO3-0.05BaTiO3-xBiFeO3(x=0~0.09)系无铅压电陶瓷,研究了BiFeO3掺杂量对其晶体结构、介电及压电性能的影响。结果表明:在所研究的组成范围内陶瓷均能形成纯钙钛矿型固溶体。介温曲线(10kHz)显示该陶瓷体系具有明显的弥散相变特征。该陶瓷体系的压电性能较Bi1/2Na1/2TiO3-BaTiO3陶瓷(d33=125pC/N)有较大提高,当x=0.05时,具有最佳的压电性能:d33=142pC/N,kp=0.29;此时εr=891,tanδ=0.046,Qm=110。     

Theoretical investigation of the electronic structure,optical, elastic,hardness and thermodynamics properties of jadeite

A detailed theoretical study of the electronic structure, optical, elastic and thermodynamics properties of jadeite have been performed by means of the first principles based on the state-of-the-art of density functional theory within the generalized gradient approximation. The optimized lattice constants and the atomic positions are in good agreement with experimental data. The total density of states and partial density of states of jadeite have been discussed. The energy gap has been calculated along the Γ direction found to be 5.338 eV, which shows that jadeite has wide direct band gap. The optical properties, such as the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, loss function and absorption coefficient for [100] and [001] directions have been described for the first time in the energy range 0–40 eV. The elastic constants, bulk modulus, Young׳s modulus, anisotropic factor and Poisson׳s ratio have been calculated. Furthermore, the Vickers hardness and Debye temperature of jadeite have been predicted. The calculated values of all above parameters are compared with the available experimental values.     

Theoretical investigation of mechanical,optoelectronic and thermoelectric properties of BiGaO3 and BiInO3 compounds

The cubic BiGaO₃ and BiInO₃ perovskite oxides have been investigated for their structural stability, mechanical and opto-electronic properties by employing the density functional theory. The exchange-correlation effects have been modeled with Perdew–Burke–Ernzerhof generalized gradient approximation, while the improved evaluation of electronic properties has been achieved by using the Tran–Blaha modified form of semi-local Becke–Johnson functional. Structural properties are calculated and the thermodynamics stability of BiGaO₃ and BiInO₃ in the cubic perovskite structure has been established in terms of enthalpies of formation. Furthermore, elastic coefficients such as C_ij, bulk modules B, anisotropy factor, shear modulus G, Young’s modulus Y, Poisson’s ratio ν, and B/G ratio are predicted. Band structure calculations reveal that investigated compounds have an indirect band gap between the occupied O 2p and unoccupied Bi 6p orbitals. The optical response of BiGaO₃ and BiInO₃ are also inspected by computing the complex dielectric function, refractive index, absorption coefficient, extinction coefficient, reflectivity and optical conductivity for radiation with energy up to 16 eV. The important thermoelectric properties of the compounds are described in terms of thermal conductivity, electrical conductivity, Seebeck coefficient and figure of merit.     

Effect of annealing temperature on structural,electrical and optical properties of spray pyrolytic nanocrystalline CdO thin films

Nanocrystalline CdO thin films were prepared onto a glass substrate at substrate temperature of 300 °C by a spray pyrolysis technique. Grown films were annealed at 250, 350, 450 and 550 °C for 2.5 h and studied by the X-ray diffraction, Hall voltage measurement, UV-spectroscopy, and scanning electron microscope. The X-ray diffraction study confirms the cubic structure of as-deposited and annealed films. The grain size increases whereas the dislocation density decreases with increasing annealing temperature. The Hall measurement confirms that CdO is an n-type semiconductor. The carrier density and mobility increase with increasing annealing temperature up to 450 °C. The temperature dependent dc resistivity of as-deposited film shows metallic behavior from room temperature to 370 K after which it is semiconducting in nature. The metallic behavior completely washed out by annealing the samples at different temperatures. Optical transmittance and band gap energy of the films are found to decrease with increasing annealing temperature and the highest transmittance is found in near infrared region. The refractive index and optical conductivity of the CdO thin films enhanced by annealing. Scanning electron microscopy confirms formation of nano-structured CdO thin films with clear grain boundary.     

K+掺杂对SnO2-LiZnVO4系湿敏陶瓷性能的影响

为了提高 SnO_2-LiZnVO_4系湿敏材料的性能,采用共沉淀法制备出 SnO_2-K_2O-LiZnVO_4系纳米湿敏粉体。考察了液相掺杂 K+对材料湿敏性能、复阻抗特性和电容特性的影响。实验结果表明,采用共沉淀法制备纳米粉体并使K+液相掺杂量为 2.5%(摩尔分数),可使湿敏材料低湿电阻小、灵敏度适中,适当的 K+添加量可明显改善 SnO_2-LiZnVO_4系纳米材料的感湿特性。     

Structural,elastic, electronic and thermodynamic properties of uranium filled skutterudites UFe4P12: First principle method

We present a theoretical study of structural, elastic, thermodynamic, and electronic properties of the uranium filled skutterudite UFe₄P₁₂. We use the full-potential linear muffin–tin orbital (FP-LMTO) method in which the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The lattice parameter at equilibrium, the bulk modulus, its pressure derivative, the elastic constants and the band structure energy of the filled skutterudite UFe₄P₁₂ are calculated and systematically compared to available theoretical and experimental data. Herein, we use the total energy variation as function of strain technique to determine independent elastic constants and their pressure dependence. Furthermore, using quasi-harmonic Debye model with phonon effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity of UFe₄P₁₂ are investigated for the first time. Band structure of UFe₄P₁₂ indicates a tendency of forming a pseudo-gap that appears above the Fermi level at Γ point. This is a unique characteristic of skutterudite, especially when a single phosphorous p-band crosses the Fermi level. The crossing band is, indeed, pushed down by the repulsion of U f-resonance states.     

Effect of substrate temperature on structural,morphological, optical and electrical properties of MnIn2S4 thin films prepared by nebulizer spray pyrolysis technique

Manganese indium sulphide (MnIn₂S₄) thin films were deposited using an aqueous solution of MnCl₂, InCl₃ and (NH₂)₂CS in the molar ratio 1:2:4 by simple chemical spray pyrolysis technique. The thin film substrates were annealed in the temperature range between 250 and 350 °C to study their various physical properties. The structural properties as studied by X-ray diffraction showed that MnIn₂S₄ thin films have cubic spinel structure. The formation of cube and needle shaped grains was clearly observed from FE-SEM analysis. The energy dispersive spectrum (EDS) predicts the presence of Mn, In and S in the synthesized thin film. From the optical studies, it is analyzed that the maximum absorption co-efficient is in the order between 10⁴ and 10⁵ cm⁻¹ and the maximum transmittance (75%) was noted in the visible and infrared regions. It is noted that, the band gap energy decreases (from 3.20 to 2.77 eV) with an increase of substrate temperature (from 250 to 350 °C). The observations from photoluminescence studies confirm the emission of blue, green, yellow and red bands which corresponds to the wavelength range 370–680 nm. Moreover, from the electrical studies, it is observed that, as the substrate temperature increases the conductivity also increases in the range 0.29–0.41×10⁻⁴ Ω⁻¹ m⁻¹. This confirms the highly semiconducting nature of the film. The thickness of the films was also measured and the values ranged between 537 nm (250 °C) to 483 nm (350 °C). This indicates that, as the substrate temperature increases, the thickness of the film decreases. From the present study, it is reported that the MnIn₂S₄ thin films are polycrystalline in nature and can be used as a suitable ternary semiconductor material for photovoltaic applications.     

Effect of rhenium doping on various physical properties of single crystals of MoSe2

Effect of rhenium doping is examined in single crystals of MoSe₂ viz. MoRe_0.005Se_1.995, MoRe_0.001Se_1.999 and Mo_0.995Re_0.005Se₂, which is grown by using the direct vapor transport (DVT) technique. The grown crystals are structurally characterized by X-ray diffraction, by determining their lattice parameters a and c, and X-ray density. Also, the Hall effect and thermoelectric power (TEP) measurements show that the single crystals exhibit a p-type semiconducting nature. The direct and indirect band gap measurements are also undertaken on these semiconducting materials.     

Effect of rhenium doping on various physical properties of single crystals of MoSe2

正Effect of rhenium doping is examined in single crystals of MoSe_2 viz.MoRe_(0.005)Se_(1.995), MoRe_(0.001)Se_(1.999) and Mo_(0.995)Re_(0.005)Se_2,which is grown by using the direct vapor transport(DVT) technique. The grown crystals are structurally characterized by X-ray diffraction,by determining their lattice parameters a and c,and X-ray density.Also,the Hall effect and thermoelectric power(TEP) measurements show that the single crystals exhibit a p-type semiconducting nature.The direct and indirect band gap measurements are also undertaken on these semiconducting materials.     

Optical,morphological and electrical studies of Zn:PbS thin films

Structural, electrical, and optical properties of undoped and Zn doped lead sulfide (PbS) thin films are benign reported in this paper. The subjected films were grown on glass substrates at 25 °C by a chemical bath deposition (CBD) method. The concentration of Zn in the deposition bath represented by the ratio [Zn²⁺]/[Pb²⁺] was varied from 0% to 5%. It was found that the film׳s grains decreased in size with increasing Zn content in the film. XRD data showed the polycrystalline nature of the film its crystal orientation peak intensities decreased with higher doping concentration of Zn. Atomic force microscopy (AFM) measurements revealed that the surface roughness of the films decreased due to zinc doping as well. However, with increasing of the dopant concentration from 0% to 5%, the average transmittance of the films varied over the range of 35–75%. The estimated optical band (E_g) gaps of undoped and Zn doped PbS thin films were in the range of 0.72–1.46 eV. Hall Effect measurements electrical resistivity, carrier concentration and Hall mobility have been determined for the titled film as functions on the Zn content within the film׳s textures. The overall result of this work suggested that the Zn:PbS film is a good candidate as an absorber layer in the modern solar cell devices.     

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1-x CoxO(where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.