Fabrication and properties of Ag/Mg<Subscript>0.2</Subscript>Zn<Subscript>0.80</Subscript>/La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO/p<Superscript>+</Superscript>-Si resistive switching heterostructure devices

Mg_0.2Zn_0.8O (MZO)/La_0.67Ca_0.33MnO (LCMO) heterostructure was deposited on p⁺-Si substrates by sol-gel spin coating technique. The Ag/MZO/LCMO/p⁺-Si devices exhibit a bipolar, reversible, and remarkable current-voltage characteristic at room temperature. An obvious multilevel resistive switching effect is observed in the devices. The dominant conduction mechanism of the devices is trap-controlled space charge limited current. The resistance ratio of high resistance state and low resistance state of the devices is about six orders of magnitude, and the degradation is invisible in the devices after 250 successive switching cycles. The present results suggest that the Ag/MZO/LCMO/p⁺-Si devices may be a potential and multilevel candidate for nonvolatile memory application.     

Infrared Emissivity of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript> with Three Different Structures

La_0.8Sr_0.2MnO₃ samples with rhombohedral, orthohombic and monoclinic structures were prepared by solid state reaction, sol-gel and co-precipitation methods, respectively. Lattice parameters, grain size, morphology, infrared absorption and emissivity of samples were investigated. The results indicated that the average crystallite size calculated from XRD result and particle size of orthohombic sample were smaller than those of the other two samples, and honeycomb shape grains were observed in orthohombic sample. Due to lower crystal symmetry, Mn-O stretching vibration peaks of the three samples shifted to higher infrared wavenumber. According to the theory of wave optics and Kirchhoff law, bigger rhombohedral sample showed higher emissivity than monoclinic one. However, due to the honeycomb structure of orthohombic sample, repeated reflection and scattering led to the increase of absorption, and orthohombic sample exhibited the highest emissivity.     

Low temperature synthesis of amorphous La<Subscript>0.7</Subscript>Zn<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> films grown on p<Superscript>+</Superscript>-Si substrates and its resistive switching properties

Amorphous La_0.7Zn_0.3MnO₃ (LZMO) films were deposited on p⁺-Si substrates by sol-gel method at low temperature of 450 °C. The Ag/LZMO/p⁺-Si device exhibits invertible bipolar resistive switching and the R _HRS/R _LRS was about 10⁴-10⁶ at room temperature which can be kept over 10³ switching cycles. Better endurance characteristics were observed in the Ag/LZMO/p⁺-Si device, the V _Set and the V _Reset almost remained after 10³ endurance switching cycles. According to electrical analyses, the conductor mechanism was in low resistor state (LRS) governed by the filament conductor and in the high state (HRS) dominated by the traps-controlled space-charge-limited current (SCLC) conductor.     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Thermoelectric Properties and Electronic Structure of Ca3Co2O6

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process.The phase composition was characterized by means of X-ray diffraction.Polycfrystalline swnples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power.The seebeck cofficient and electrical conductivity of the samples were measured from 450K up to 750 K.The results show that the Seebeck coefficient increases with the increasing temperature.The electronic structures were calculated using the self-cwtsistent full-potential linearized augmentedc plane-wave (LAPW) method within the density functional theory.The relationship between thermoelectric property and electronic structures was discussed.     

Phase structure and electrical properties of La<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped BiInO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ceramics with high curie temperature

The phase structure and electrical properties of pure and La2O3-doped Bi-InO3-PbTiO3 （BI-PT） ceramics were studied respectively. In （1 -x）BI-xPT （x=0.72-0.80） ceramics, the stability of tetragonal phase increased with increasing x, and pure perovskite structure was obtained for x=-0.80 ceramics. The phase transition temperature range was between 575 ℃ and 600 ℃ for x=0.72-0.80 ceramics, higher than that of PT （-490 ℃）. The c/a ratio almost linearly decreased with increasing La2O3 content in x-0.80 ceramics. It is believed that Pb^2＋ vacancies were formed by La^3＋ substituting Pb^2＋ in La2O3-doped BI-PT ceramics. Tc shifted to lower temperature by 30 ℃/mol% La2O3. The maximum dielectric constant 8557 around 559 ℃ was exhibited in 0.5mol%-doped BI-0.80PT ceramics. La2O3-doped ceramics could be poled resulting from decreasing of c/a ratio and improving of dielectric loss and resistivity. The maximum piezoelectric coefficient d33 was 12 pC/N for 2mol%-doped BI-0.80PT ceramics.     

Orientation of Bi<Subscript>3.2</Subscript>La<Subscript>0.8</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric thin films with different annealing schedules

Fatigue-free Bi_3.2La_0.8Ti₃O₁₂ ferroelectric thin films were successfully prepared on p-Si (100) substrates using metalorganic solution deposition process. The orientation and formation of 5-layers thin films were studied under different processing conditions using XRD. Experimental results indicate that increase in annealing time at 700 °C after preannealing for 10 min at 400 °C can remarkably increase (200)-orientation of the films derived from the precursor solutions with two contents of citric acid. Meanwhile, high content of citric acid increases the film thickness and is conducive to the a-orientation of the films with the preannealing, and low concentration of the solution is conducive to the c-orientation of the films without the preannealing.     

Microstructures and fatigue-free properties of the La<Superscript>3+</Superscript> and Nd<Superscript>3+</Superscript> doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by modified sol-gel technique

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were fabricated on Pt/TiO₂/SiO₂/Si (100) substrates by a modified sol-gel technique. X-ray diffraction indicated that these films were of single phase with random polycrystalline orientations. The surface morphologies of the films were observed by scanning electron microscope, showing uniform, dense films with grain size of 50–100 nm. Well-saturated hysteresis loops of the films were obtained in metal-ferroelectric-metal type capacitors with Cu top electrodes at an applied voltage of 400 kV/cm, giving the remanent polarization (2P _r) and coercive field (2E _c) values of the films of 25.1 μC/cm² and 203 kV/cm for BLT, and 44.2 μC/cm² and 296 kV/cm for BNT, respectively. Moreover, these capacitors did not show fatigue behaviors after up to 1.75×10¹⁰ switching cycles at the test frequency of 1 MHz, suggesting a fatigue-free character. The influences of the La³⁺ and Nd³⁺ doping on the properties of the films were comparatively discussed. Supported by the National Key Basic Research and Development Program of China (Grant No. 2006CB932305) and the Natural Science Foundation of Hubei Province, China (Grant No. 2004ABA082)     

Structure and Electric Properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 Systems

The structural, dielectric and piezoelectric properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 ceramics were investigated for the compositional range, x=0.02, 0.04, 0.06, 0.08, 0.10. The samples were synthesized by a conventional solid-state reaction technique. All compositions show a single perovskite structure, and X-ray powder diffraction patterns can be indexed using a rhombohedral structure. Lattice constants and lattice distortion increase while the amount of BaTiO3 increases. The X-ray diffraction results show the morphotropic phase boundary （MPB） of （1-x）（Bi1/2Na12） TiO3-xBaTiO3 exists in near x=0.06-0.08. Temperature dependence of dielectric constant eT33/ε0 measurement reveals that all compositions experience one structural phase and two ferroelectric phases transition below 400℃： rhombohedral （or rhombohedral plus tetragonal） ferroelectric phase ←→ tetragonal antiferroelectric phase ←→ tetragonal paraelectric phase. Relaxor behaviors exist in the course of ferroelectric to antiferroelectric phase transition. Dielectric and piezoelectric properties are enhanced in the MPB range for （ 1-x）（Bi1/2Na1/2）TiO3-xBaTiO3.     

Dielectric Properties of B2O3 Doped MgTiO3-CaTiO3 System Ceramics

The dielectric ceramics with a main crystal phase of MGTiO3 and additional crystal phase of CaTiO3 were prepared by the conventional electronic ceramics technology .the strucures of MgTiO3 are ilmenitetype,and belong to hexagonal syngony.the ratio of MgTiO3 to Ca TiO3 doping on the dielectric properties of MGTiO3-CaTiO3(MCT)ceranics were inrestigated.the addition of B2O3 decreases the sintering temperatnre and results in rapid desification without obrious negative effect on the Q values of the system(Q=1/tan ).B2O3 exists as liquid phase in the sintering process,promoting the reactions as a singering agent.     

Effect of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass addition on the microwave dielectric properties of BaO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The effect of ZnO-B₂O₃(ZB) glass addition on the sintering behavior, microstructures and microwave dielectric properties of BaO-Nd₂O₃-TiO₂-Bi₂O₃ (BNTB) system was investigated with the aid of X-ray diffraction, scanning electron microscopy and capacitance meter. It is found that the ZB glass addition, acting as a sintering aid, can effectively lower the sintering temperature of BNTB system to 850 °C. The dielectric constant of BNTB-ZB ceramics increases with the increase of soaking time and the value of dielectric loss decreased with increasing soak time. The optical dielectric properties at 1 GHz of ɛ=74, tan δ=4×10⁻⁴, and TCC=25 ppm/°c were obtained for the BNTB system doped with 25 wt% ZB glass sintered at 850 °C for 2 h, representing that the BNTB-ZB ceramics could be promising for multilayer low temperature co-fired ceramics applications.     

Enhanced Ferroelectric Polarization in Laser-ablated Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films by Controlling Preferred Orientation

Polycrystalline Bi₄Ti₃O₁₂ thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO₂/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi₄Ti₃O₁₂ thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm², respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm²) was obtained for the Bi₄Ti₃O₁₂ thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi₄Ti₃O₁₂ films.     

Optimization of SO<Subscript>3</Subscript> content in blended cementitious materials

Experimental investigation was conducted on the effects of gypsum types and SO₃ content on the fluidity and strengths of different cementitious systems. The experimental results show that influences of gypsum in various cementitious materials are different. For cementitious materials blended with various proportions of slag-fly ash and 5% gypsum content, influences of gypsum and calcined gypsum on the fluidity and flexural/compressive strength are similar. It is revealed that “combination effect” and “synergistic effect” of slag and fly ash play an important role during hydration. For cementitious materials with 45% clinkers, 30% slag, 20% fly ash and 5% limestone, the optimized SO₃ contents in gypsum and calcined gypsum are 3.13% and 3.51% respectively and the optimized gypsum content is 6.5%. While both of them are blended, the optimum ratio of gypsum to calcined gypsum is 40%:60% (total gypsum content 6.5%), correspondingly the optimum ratio of SO₃ is 19.3%:32. 4%. CHEN Mei-zhu : Born in 1974 Funded by Hubei Bureau of Science and Technology of China (981P0202)     

Effect of the silicon powder content on the properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiC-Me composites

By means of transient plastic phase process, the Al₂O₃-SiC-Me composites were produced throungh adding metal aluminium and silicon-powder to Al₂O₃-SiC materials. Under the condition of the same content of silicon and aluminium mixed-powder, the effect of silicon powder addition on properties of Al₂O₃-SiC-Me composites was studied by means of XRD and EPMA analyses in the temperature range of 300°–1600°C. The results indicated that the content of metal phase in the sample at 1600°C increases with increasing silicon powder content. At the same time, when the temperature is lower than 1100°C, the strength of samples gradually increases with increasing temperature. However when the temperature is higher than 1100°C, the strength of samples gradually decreases with increasing temperature, and this change is very small. The results also indicated that at the same sintering temperature, the sample with 6% silicon powder has the maximum strength. Supported by the Chen Yunbo Academician Fund (Grant No. 2007CY021)     

Improved Breakdown Strength in (Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>)<Subscript>0.85</Subscript>Bi<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> Ceramics with Addition of CaZrO<Subscript>3</Subscript> for Energy Storage Application

(Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramics doped with x wt%CaZrO₃ (x= 0-10) were synthesized by solid-state reaction method. The effects of CaZrO₃ amount on the dielectric properties and structure of (Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramics were investigated. X-ray diffraction results indicated a pure cubic perovskite structure for all samples and that the lattice parameter increased till x=5 and then slightly decreased. A homogenous microstructure was observed with the addition of CaZrO₃. Dielectric measurements revealed a relaxor-like characteristic for all samples and that the diffusivity γ reached the maximum value of 1.78 at x=5. With the addition of CaZrO₃, the dielectric constant dependence on electric field was weakened, insulation resistivity enhanced and dielectric breakdown strength improved obviously and reached 19.9 kV/mm at x=7.5. In virtue of low dielectric loss (tan δ<0.001 5), moderate dielectric constant (ε_r >1 500) and high breakdown strength (E_b >17.5 kV/mm), the CaZrO₃ doped (Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramic is a potential candidate material for high power electric applications.     

Effects of LaNiO<Subscript>3</Subscript> interlayer on the microstructures and electrical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>Ti<Subscript>0.99</Subscript>Mn<Subscript>0.01</Subscript>O<Subscript>3</Subscript> multilayer

The aim of this work was to investigate the effects of low-resistivity interlayer on the physical properties of periodic Ba_0.9Sr_0.1Ti_0.99Mn_0.01O₃ (BSTM) multilayers prepared by a chemical solution deposition method. A LaNiO₃ (LNO) layer was inserted into the periodic BSTM multilayer artificially to form a sandwiched configuration of BSTM/LNO/BSTM. The capacitances at low frequencies (<100 kHz) of the sandwiched multilayer are significantly enhanced compared to that of the pure BSTM multilayer. The space charge accumulated at the LNO layer was proposed to explain the enhancement based on Maxwell-Wagner (M-W) model. However, LNO interlayer leads to an increase in the leakage current. A non-Ohmic conduction region is observed for BSTM/LNO/BSTM multilayer when the electric field exceeds 100 kV/cm. The results offer a new approach to achieve dielectric films with high dielectric constant.     

Effects of NaNbO3-Co2O3 Co-additive on the Properties of PZN-PZT Ceramics

NaNbO3-Co2O3 co-added PZN-PZT （PZCNNT） ceramics were prepared using conventional solid state reaction. The piezoelectric and dielectric properties were measured. The experimental results show that the addition of 0.3mo1% Co2O3 leads to low dielectric loss （tgδ） in PZCNNT ceramics and the proper addition of NaNbO3 not only improves piezoelectric properties but also decreases intensively dielectric loss and mechanical loss. The optimal ceramic having d33=310 pC/N, kp=0.59, εr=985, tgδ=0.0034, Qm=1380 was obtained.     

Synthesis and characterization of a new Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> pillared triple-layered perovskite KSr<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>10</Subscript>

A n-Hexyl NH₃Sr₂Nb₃O₁₀ is obtained by the stepwise ion-exchange reaction, then is dispersed in aqueous solution of trinuclear acetato-hydroxo iron (III) nitrate, [Fe₃(OCOCH₃)₇OH·2H₂O]NO₃, and the interlayer potassium cations of the perovskite niobate are exchanged with the partially hydrolyzed trinuclear acetato complex ions. On heating, the exchanged complex ions are converted into iron oxide pillars which keep the perovskite sheets apart. The product is characterized by XRD, SEM, EDAX and surface area measurement respectively. Zhang Hui: Born in 1970 Funded by the National Natural Science Foundation of China (No. 50002007), Major Program of Ministry of Education (No. 0201) and Open Foundation of State Key Lab of Advanced Tech. for Materials Synthesis and Processing.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> content on residual stress and properties of CAS glass-ceramics

The structure and properties of the glass-ceramics were tested with X-ray diffraction testing instrument,correlative software,and other modern testing means.Then the effect of Al2O3 content on internal stresses in CaO-Al2O3-SiO2 glass-ceramics was studied deeply.In order to study the relationship of Al2O3 to the residual stress of CaO-Al2O3-SiO2 glass-ceramics,X-ray diffraction ＂sin2ψ＂ was used.The means utilized the x radial incidence produced from cathode radial tube,and took the space between crystals as measurement of strain.When the stresses produced,the space between crystals changed and the diffraction peak moved during Bragg diffraction.The magnitude of movement is related to the stresses.The experimental results show the residual stress is considerably high and Al2O3 can influence the mechanical properties of this material hugely.     

Conformation of Organic Chain in Phase Transition of Hybrid （Cl2H25NH3）2MnCl4

The structural change in phase transition of hybrid （Cl2H25NH3）2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry （TG） and differential scanning calorimetry （DSC）, infrared spectrum （IR） and X-ray diffraction （XRD）. The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond （noted as GTG＇TGTG＇TGTG＇T）.