Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

Roles of Nano-Domain Switching and Non-180° Domains in Enhancing Local Piezoelectric Responses of Highly (100)-Oriented Pb(Zr_(0.60)Ti_(0.40))O_3 Thin Films

Ferroelectric Pb(Zr_(0.60)Ti_(0.40))O_3 thin films deposited on the niobium-doped SrTiO_3 and Pt(111)/Ti/SiO_2/Si substrates are fabricated by a sol-gel method.X-ray diffraction indicates that the films have a 'cube-on-cube'growth with highly(100)preferred orientation and good surface qualities.Using piezoelectric force microscopy,we investigate domain structures and butterfly amplitude loops of ferroelectric thin fims.The results indicate that the film deposited on Nb:SrTiO_3 has both kinds of 180° polarizations perpendicular or parallel to the surface while the film deposited on Pt/Ti/SiO_2/Si has irregular phase differences.Excellent piezoelectric polarization are observed in the films on niobium-doped SrTiO_3 with local d_(33)~* values around 45 pm/V three times more than that of the films around 13 pm/V deposited on Pt(111)/Ti/SiO2/Si. Our findings emphasize that nanodomain switching ability and non-180° domains will contribute significantly to enhance piezoelectric responses of ferroelectric thin films.     

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5Na0.5NbO3- 0.04LiSbO3 lead-free piezoelectric ceramics

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5+xNa0.5+xNbO3- 0.04LiSbO3 lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d33 = 187 pC/N at x = 0.0075, coinciding with the maximum of the grain size and the apparent density at x = 0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K0.5+xNa0.5+xNbO3-0.04LiSbO3. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K++Na+) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K0.5Na0.5NbO3-based lead-free ceramics with enhanced electrical properties.     

Growth of high quality Ce~(3 ):YAP and (Ce~(3 ) Nd~(3 )): YAP single crystals

The effect of melt pretreatment of Ce~(3 ): YAP and (Ce~(3 ) Nd~(3 )): YAP and their growth ambient gases on the quality of the crystals are described. Firstly, a superheating pretreatment of YAP melt is adopted in a nitrogen atmosphere containing a little oxygen to eliminate carbon; then the YAP melt is superheated in a reduction atmosphere to fully reduce Ce~(4 ) ions into Ce~(3 ) ions in the melt. Finally, in a growth atmosphere of pure nitrogen, high quality Ce~(3 ): YAP and (Ce~(3 ) Nd~(3 )): YAP single crystals with high Ce~(3 ) concentration with only few light scattering centers were grown.     

Phase Transition and High Piezoactivity of Sr Doped Lead-Free （Na0.53K0.422Li0.048） （Nb0.89Sb0.06Wa0.05）O3 Ceramics

Lead-free piezoelectric ceramics （Na0.53K0.422Li0.048 ） （Nb0.89Sb0.06 Ta0.05 ）03 （NKLNST） ＋ x tool SrCO3 are prepared by conventional solid state sintering method. The specimens with pure perovskite structure show tetragonal phase at x 〈 0.01, and become pseudo-cubic phase at x 〉 0.02. A lattice parameter discontinuity is found in the specimens with 0.004 〈 x 〈 0.0075, along with a great improvement in piezoactivity. The 0.004 mol SrCO3 added NKLNST ceramics possesses outstanding performances of kp = 0.53, kt = 0.26, and d33=309 pC/N. Moreover, the Sr^2＋ modification inhibits the gra/n growth, decreases the Curie temperature, and induces a diffuse phase transition.     

Different effect of NiMnCo or FeNiCo on the growth of type-Ⅱa large diamonds with Ti/Cu as nitrogen getter

In order to synthesize high-quality type-Ⅱa large diamond, the selection of catalyst is very important, in addition to the nitrogen getter. In this paper, type-IIa large diamonds are grown under high pressure and high temperature(HPHT) by using the temperature gradient method(TGM), with adopting Ti/Cu as the nitrogen getter in Ni_(70)Mn_(25)Co_5(abbreviated as NiMnCo) or Fe_(55)Ni_(29)Co_(16)(abbreviated FeNiCo) catalyst. The values of nitrogen concentration(N_c) in both synthesized high-quality diamonds are less than 1 ppm, when Ti/Cu(1.6 wt%) is added in the FeNiCo or Ti/Cu(1.8 wt%) is added in the NiMnCo. The difference in solubility of nitrogen between both catalysts at HPHT is the basic reason for the different effect of Ti/Cu on eliminating nitrogen. The nitrogen-removal efficiency of Ti/Cu in the NiMnCo catalyst is less than in the FeNiCo catalyst. Additionally, a high-quality type-Ⅱa large diamond size of 5.0 mm is obtained by reducing the growth rate and keeping the nitrogen concentration of the diamond to be less than 1 ppm, when Ti/Cu(1.6 wt%) is added in the FeNiCo catalyst.     

Characterization of the BaBiO3-doped BaTiO3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with Tc=155℃

BaBiO 3-doped BaTiO3(BB-BT) ceramic,as a candidate for lead-free positive temperature coefficient of resistivity (PTCR) materials with a higher Curie temperature,has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature,Tc=155℃,which is higher than that of BaTiO3(≤130℃). Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current (AC) resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data,the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature,indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency,the conduction mechanism is also discussed for a BB-BT ceramic system.     

Dielectric Enhancement and Maxwell—Wagner Effect in Polycrystalline BaTiO3／Ba0.2Sr0.8TiO3 Multilayered Thin Films

Polycrystalline BaTiO3/Ba0.2Sr0.8TiO3 multilayer thin films were fabricated by pulsed laser deposition onto Pt/Ti/SiO2/Si substrates with various stacking periodicities.The dielectric constant of the films was obviously enhanced with the decrease of the individual layer thickness,while the dielectric loss was kept at a low level comparable to that of the pure Ba0.6Sr0.4TiO3 thin films.The Maxwell-Wagner model is used to explain the experimental data.     

Growth characteristics of type IIa large single crystal diamond with Ti/Cu as nitrogen getter in FeNi–C system

High-quality type IIa large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi–C system at temperature ranging from 1230℃ to 1380℃ and at pressure 5.3–5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the Fe Ni–C system to investigate the best ratio for high-quality type IIa diamond. Then, the different content of nitrogen getter Ti/Cu(Ti : Cu = 4 : 3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared(FTIR), are analyzed by optical microscopy(OM) and scanning electron microscopy(SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter.Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25℃ higher than that of type Ib diamond.With the increase of the content of Ti/Cu(Ti : Cu = 4 : 3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm.The SEM results show that the synthesized crystals are mainly composed by(111) and(100) surfaces, including(311)surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type IIa diamond.     

Model of output characteristics of giant magnetoresistance(GMR) multilayer sensor

In this paper, the giant magnetoresistance(GMR) multilayer sensor is fabricated with a Wheatstone bridge, and it exhibits excellent performance with a sensitivity of 2.8349 mV/(V/Oe)(1 Oe = 79.5775 A·m~(-1)) and a saturation field of 26 Oe along the sensitive axis. The GMR sensor is also characterized in a high magnetic field. The sensitivity decreases from 2.8349 mV/(V/Oe) at an angle of 0°to 0.0175 mV/(V/Oe) at an angle of 90°. Then, the sensor is placed in a series of rotating magnetic fields. We propose a model to express the output characteristics of the GMR multilayer sensor. The transfer curves of the sensor can be shown as two exactly symmetrical circles with an increasing radius when the magnetic field increases. The experimental results are consistent with the simulation results of the model. The advantage of this model is that it is simpler and more intuitive.     

Elastic,dielectric, and piezoelectric characterization of 0.92Pb(Zn1/3Nb2/3)O3-0.08PbTiO3 single crystal by Brillouin scattering

In this paper,a complete set of elastic,piezoelectric,and dielectric constants of high-quality tetragonal poled0.92Pb(Zn_(1/3)Nb_(2/3))O_3-0.08PbTiO_3 single crystal grown by the modified flux method is determined using high-resolution Brillouin scattering.A comparison is made between the results obtained by a hybrid method combining ultrasonic and resonant techniques and the results obtained by the Brillouin scattering.The elastic,piezoelectric,and dielectric constants obtained by the two methods are similar.The Brillouin spectrum consists of one longitudinal and two transverse acoustic phonon modes,and the variations of the Brillouin shifts,the full widths at half maximum,and the scattering intensities of these modes with scattering angle 9 are investigated.In particular,the transverse acoustic phonon mode at the lowfrequency becomes markedly soft from 28.2 GHz to 18.4 GHz and broadens gradually with the increase of θ,while its intensity decreases gradually as compared with that of the original one.The possible origins of the results are discussed.     

High sensitivity gravimetric sensor made of unidirectional carbon fiber epoxy composite on （1-x）Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystal substrate

We have derived a general formula for sensitivity optimization of gravimetric sensors and have used it to design a high sensitivity gravimetric sensor using unidirectional carbon fiber epoxy composite(CFEC) waveguide layer on(1- x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT) single crystal substrate with the carbon fibers parallel to the x1 and x2axes, respectively. The normalized maximum sensitivity Sfm λ maxexhibits an increasing tendency with the decrease of(h/λ)optand the maximum sensitivity Sfm λ maxincreases with the elastic constant cE66 of the piezoelectric substrate material. For the CFEC/[011]c poled PZN-7%PT single crystal sensor configuration, with the carbon fibers parallel to the x1 axis at λ = 24 μm, the maximum sensitivity Sfm maxcan reach as high as 1156 cm2/g, which is about three times that of a traditional SiO2/ST quartz structure gravimetric sensor. The better design selection is to have the carbon fibers parallel to the direction of propagation of Love wave in order to obtain the best sensitivity.     

1984年CUSPEA试题(三)(英文)

Solve 5 of the following 6 problems.C1. (a ) Consider the emission or absorption of visible light by the molecules of a hotgas. Derive an expression for the frequency distribution F(v) expected for aspectral line of central frequency v0 due to the Doppler broadening. Assume an ideal gas at temperature T with molecular weight M.Consider a vessel filled with argon gas at a. pressure of 10 Torr (1 Torr=l mm of mercury) and a temperature of 2000℃. Inside the vessel is a smallpiece of sodium w…     

Structure instability-induced high dielectric properties in[001]-oriented 0.68Pb(Mg_(1/3)Nb_(2/3))O_3–0.33PbTiO_3 crystals

The structure evolution and origin of ultrahigh dielectric properties have been investigated in the low temperature range from 300 K to 5 K for [001]-oriented 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3–0.33PbTiO_3(PMN–33 PT) crystal. The experimental results reveal that a short-range ordered monoclinic MAis the dominant phase at ambient temperature. As the temperature drops below 270 K, the MAtransforms into monoclinic MC, and the MCremains stable until 5 K. Although no phase transition occurs from 5 K to 245 K, polar nanoregions(PNRs) display visible changes. The instability of PNRs is suggested as responsible for the low temperature relaxation. The ultrahigh dielectric constant at room temperature is associated with the instability of local structure and phase transition. Our research provides an insight into the design of high-performance ferroelectric materials.     

Effects of （LiCe） co-substitution on the structural and electrical properties of CaBi2Nb209 ceramics

The piezoelectric,dielectric,and ferroelectric properties of the(LiCe) co-substituted calcium bismuth niobate(CaBi2Nb2O9,CBNO) are investigated.The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan δ decreased.This makes poling using(LiCe) co-substitution easier.The ceramics(where represents A-site Ca2+ vacancies,possess a pure layered structure phase and no other phases can be found.The Ca0.88(LiCe)0.04 0.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties,with piezoelectric coefficient(d 33) and Curie temperature(TC) found to be 13.3 pC/N and 960 C,respectively.The dielectric and piezoelectric properties of the(LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours.This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.     

Optimization of TiO_2/Cu/TiO_2 multilayers as a transparent composite electrode deposited by electron-beam evaporation at room temperature

Highly transparent indium-free composite electrodes of Ti O2/Cu/Ti O2 are deposited by electron-beam evaporation at room temperature. The effects of Cu thickness and annealing temperature on the electrical and optical properties of the multilayer film are investigated. The critical thickness of Cu mid-layer to form a continuous conducting layer is found to be 11 nm. The multilayer with a mid-Cu thickness of 11 nm is optimized to obtain a resistivity of 7.4×10-5Ω·cm and an average optical transmittance of 86% in the visible spectral range. The figure of merit of the Ti O2/Cu(11 nm)/Ti O2 multilayer annealed at 150ΩC reaches a minimum resistivity of 5.9×10-5Ω·cm and an average optical transmittance of 88% in the visible spectral range. The experimental results indicate that Ti O2/Cu/Ti O2 multilayers can be used as a transparent electrode for solar cell and other display applications.     

boldmath Characterization of the BaBiO3-doped BaTiO3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with Tc=155℃

BaBiO₃-doped BaTiO₃ (BB-BT) ceramic, as a candidate for lead-free positive temperature coefficient of resistivity (PTCR) materials with a higher Curie temperature, has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature, T_c=155 ℃, which is higher than that of BaTiO₃ ( ≤ 130 ℃). Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current (AC) resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data, the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature, indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency, the conduction mechanism is also discussed for a BB-BT ceramic system.     

Magnetic properties of L1_0 FePt thin film influenced by recoverable strains stemmed from the polarization of Pb(Mg_(1/3)Nb_(2/3))O_3–PbTiO_3 substrate

The magnetic properties and magnetization reversible processes of L1_0 FePt(3 nm)/Pb(Mg_(1/3)Nb_(2/3))O_3–PbTiO_3(PMN–PT) heterostructure were investigated by using the phase field model. The simulation results show that the magnetic coercivities and magnetic domains evolution in the L1_0 FePt thin film are significantly influenced by the compressive strains stemming from the polarization of single crystal PMN–PT substrate under an applied electric field. It is found that the magnetic coercivities increase with increasing of the compressive strain. A large compressive strain is beneficial to aligning the magnetic moments along the out-of-plane direction and to the enhancement of perpendicular magnetic anisotropy. The variations of magnetic energy densities show that when compressive strains are different at the magnetization reversible processes, the magnetic anisotropy energies and the magnetic exchange energies firstly increase and then decrease, the negative demagnetization energy peaks appear at coercivities fields, and the magnetoelastic energies are invariable at large external magnetic field with the energy maximum appearing at coercivities fields. The variations of the magnetoelastic energies bring about the perpendicular magnetic anisotropy so that the magnetoelastic energy is lower at the large external magnetic fields, whereas the appearance of magnetoelastic energy peaks is due to the magnetization-altered direction from the normal direction of the plane of the L1_0 FePt thin film at coercivities fields.     

Effects of Al and Ti/Cu on Synthesis of Type-IIa Diamond Crystals in Ni70Mn25Co5-C System at HPHT

High-quality type-Ⅱa gem diamond crystals are successfully synthesized in a NiToMn25Co5-C system by temperature gradient method （TGM） at about 5.5 GPa and 1560 K. Al and Ti/Cu are used as nitrogen getters respectively. While nitrogen getter Al or Ti/Cu is added into the synthesis system, some inclusions and caves tend to be introduced into the crystals. When Al is added into the solvent alloy, we would hardly gain high-quality type-Ⅱa diamond crystals with nitrogen concentration Nc 〈 1 ppm because of the reversible reaction of Al and N at high pressure and high temperature （HPHT）. Piowever, when Ti/Cu is added into the solvent alloy, high-quality type-Ⅱa diamond crystals with Nc 〈 1 ppm can be grown by decreasing the growth rate of diamonds.     

Properties of Co-Doped 0.92（Na0.5Bi0.5） TiO3-0.08BaTiO3 Lead-Free Ceramics

Lead-free piezoelectric ceramics 0.92（Bi0.5Na0.5）TiO3-0.08BaTiO3 ＋ xmol% Co3＋ （BNBT-Co, x = 0-8） are prepared by the solid state reaction method. Effects of the amount of Co^3＋ on the electrical properties and phase transition are studied. The results indicate that the addition of Co^3＋ enhances the mechanical quality factor Q^3＋ significantly, whereas the dissipation factor tanδ has a minimum value at x = 3.5. Meanwhile, addition of Co^3＋ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92（Bio.aNao.5） TiO3-0.08BaTiO3＋3.5 moi% Co^3＋ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant d33 = 106pC/N, planar electromechanical coupling kp =10% and dissipation factor tanδ = 1.1% at 1 kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of ε33^T vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co^3＋, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.