Molecular mobility in piezoelectric hybrid nanocomposites with 0–3 connectivity: Volume fraction influence

Thermo Stimulated Current and Dynamic Dielectric Spectroscopy studies were carried out on hybrid ferroelectric Polyamide 11/Barium Titanate to investigate dielectric relaxation modes. The correlated results obtained by both methods allow us to describe precisely the molecular mobility of this 0–3 nanocomposite; in this work we will focus on the influence of the 700 nm nanoparticles volume fraction. The dielectric spectroscopy shows that the molecular mobility associated with the liquid dynamic is not influenced by the volume fraction. The evolution of low frequency relaxation, observed by depolarization currents techniques, have been attributed to the decrease of Cooperative Rearranging Region size and the increase of intra/inter macromolecular interactions in the soft amorphous phase.     

Electroactive influence of ferroelectric nanofillers on polyamide 11 matrix properties

Barium titanate ceramic powders have been incorporated in polyamide 11 to form homogeneous dispersion of particles in the matrix. Barium titanate/polyamide 11 nanocomposites have been synthesized using a solvent casting method with ultrasonic stirring to homogeneously disperse inclusions in the matrix. Composites with volume fraction of barium titanate ϕ ranging from 0.01 to 0.4 were elaborated. Films were fabricated using a hot press method. Only the inclusions were poled in the matrix to form a ferroelectric particles/unpoled matrix composite. Interactions between the particles and the matrix, pyroelectric and piezoelectric response were studied as a function of ϕ by dynamic dielectric spectroscopy. Composites show interesting pyro-piezoelectric activity. Pyroelectric merit factor increases linearly and it reaches a limit value of 0.3 for a volume fraction ϕ = 0.1.     

Correlation of ion dynamics and structure in superionic glasses and nanocomposites

Ion dynamics of AgI-doped Ag₂O–TeO₂ glasses and Ag₂S doped glass nanocomposites have been studied using impedance spectroscopy and correlated with their structures investigated using Fourier transform infrared spectroscopy. The composition dependences of the dc conductivity and the activation energy of these glasses and nanocomposites have been compared with those of AgI-doped silver phosphate and borate glasses. We have studied the ion dynamics in the framework of the power-law and the electric modulus formalisms. We have established a correlation between the crossover rate of the mobile silver ions and the rearrangement of the structural units of glassy networks. The scaling of the conductivity spectra has been used to interpret the temperature and composition dependence of the relaxation dynamics. Analysis of the dielectric relaxation in the framework of modulus formalism indicates an increase in ion–ion cooperation in the glass compositions with increasing AgI content.     

Inorganic-Organic Nanocomposite Assembly Using Collagen as Template and Sodium Tripolyphosphate as A Biomimetic Analog of Matrix Phosphoprotein

Nanocomposites created with polycarboxylic acid alone as a stabilization agent for prenucleation clusters-derived amorphous calcium phosphate exhibit non-periodic apatite deposition. In the present study, we report the use of inorganic polyphosphate as a biomimetic analog of matrix phosphoprotein for directing polyacrylic acid-stabilized amorphous nanoprecursor phases to assemble into periodic apatite-collagen nanocomposites. The sorption and desorption characteristics of sodium tripolyphosphate to type I collagen was examined. Periodic nanocomposite assembly with collagen as a template was demonstrated with TEM and SEM using a Portland cement-based resin composite and a phosphate-containing simulated body fluid. Apatite was detected within the collagen at 24 hours and became more distinct at 48 hours, with prenucleation clusters attaching to the collagen fibril surface during the initial infiltration stage. Apatite-collagen nanocomposites at 72 hours were heavily mineralized with periodically-arranged intrafibrillar apatite platelets. Defect-containing nanocomposites caused by desorption of TPP from collagen fibrils were observed in regions lacking the inorganic phase.     

Dielectric spectroscopy of natural rubber-cellulose II nanocomposites

Nanocomposite materials obtained from natural rubber (NR) reinforced with different amounts of cellulose II nanoparticles (in the range of 0 to 30 phr) are studied by dielectric spectroscopy (DS). For comparative purposes the pure materials, NR and cellulose, are also investigated. The dielectric spectra of the nanocomposites exhibit: (a) two overlapped α-relaxations associated respectively with the dynamic glass transitions of NR (faster process) and of the lipid present in NR; (b) a β-relaxation associated with local chain dynamics of cellulose and (c) a relaxation process associated to the presence of traces of water in cellulose. The spectra exhibit conductivity phenomena at low frequencies and high temperatures. The samples were also studied in the dry state. An explanation is given concerning the cellulose effect on the dielectric properties of the dry and wet nanocomposites.     

Mechanical improvement of P(VDF-TrFE) /nickel nanowires conductive nanocomposites: Influence of particles aspect ratio

Nickel nanowires with high aspect ratio (250) were elaborated and incorporated into poly(vinylidene difluoride-trifluoroethylene) up to 30 vol% via solvent mixing way. These nanocomposites are characterized by a conductive behavior with a high electrical conductivity value (10² S m^?1) above a very low percolation threshold (0.75 vol% of metallic nanowires). The introduction of nanowires strongly depressed the matrix crystallinity. Static and dynamic mechanical analysis have been realized at low nanowire volume fraction (< 10 vol%). Below 5 vol% of nanowires, nanocomposites remain ductile. The dynamic mechanical properties are related to the volume fraction of nanowires. A strong increase of the viscoelastic contribution related to the increase of the percentage of amorphous phase is observed. The major effect is the increase of the rubbery modulus. The highest increase of 300% is obtained for only 5 vol% of nanowires; it represents an original mechanical result for low filled composites. The dependence versus nanowire content has been described by adapting the Halpin–Tsai model to high aspect ratio filler. Metallic nanowires create additional entanglements that are randomly distributed in the rubbery polymeric matrix. With their low percolation threshold, metallic nanowires based nanocomposites constitute a new class of multifunctional materials with a high conductivity associated with a ductile polymer matrix characterized by a high rubbery modulus.     

Dielectric properties of ion plated titanium oxide thin films

Titanium oxide thin films have been deposited by an ion plating technique under rf glow. The structure of the deposited film has been found to be amorphous and the composition has been analysed by IR spectrum. Aging and annealing studies of the titanium oxide capacitors have been made. The dielectric constant of the film at 1 kHz has been estimated to be 12.4. The dependence of the capacitance and dielectric loss on frequency and temperature have been studied, and the results are discussed. The temperature coefficient of the capacitance has also been calculated.     

Physical structure of P(VDF-TrFE)/barium titanate submicron composites

Dynamic Dielectric Spectroscopy and Thermo Stimulated Current were used to investigate of the dielectric relaxation of hybrid Poly(vinylidene-fluoride-trifluoroethylene)/barium titanate 700 nm composites with 0–3 connectivity. The results obtained by this method allow us to describe the physical structure of these composites in the glassy state at a nanometric scale. The decrease of the activation enthalpies and activation entropies involved in the dynamics of the α relaxation is attributed to: the decrease of Cooperative Rearranging Region sizes and an increase of intra/inter macromolecular interactions in the amorphous phase with the volume fraction.     

Dielectric properties of natural rubber/chitosan blends: Effects of blend ratio and compatibilization

The electrical properties of blends from natural rubber and chitosan have been studied in the frequency range of 10²-10⁶ Hz. Blending of chitosan with a non-polar polymer such as natural rubber is expected to improve the dielectric performance of chitosan, by reducing the polarity. This paper presents the results of dielectric properties of natural rubber/chitosan blends. Special attention has been paid to analyze the effect of blend composition, vulcanization of the major phase and the influence of compatibilization using maleic anhydride on the dielectric properties of natural rubber/chitosan blends. The temperature dependence of dielectric properties on the blends has also been studied.     

Dielectric properties of Zr-Sn-Ti-O thin films prepared by pulsed laser deposition

Zr_0.26Sn_0.23Ti_0.51O₂ (ZSTO) films with a dielectric constant of about 40 have been prepared directly on silicon substrates by pulsed laser deposition at 600 °C. TEM observation showed that the as-deposited films are amorphous. Differential thermal analysis showed that the ZSTO films crystallize at about 620 °C. Capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor (MOS) composed of Pt/ZSTO/Si prepared at different deposition temperature have been measured. The EOT of the MOS structures with the same ZSTO physical thickness increased slightly when the deposition temperature increased. The EOT is about 4.2 nm for the 40 nm ZSTO deposited at 600 °C. The leakage current characteristics of ZSTO films for the as deposited, post-annealed in oxygen ambient and post-annealed in nitrogen ambient by rapid thermal annealing have been studied comparatively. The films post-annealed in nitrogen ambient have the lowest leakage current and the as-deposited films have the largest leakage current characteristics. It is proposed that amorphous Zr-Sn-Ti oxide stabilized at 600 °C is a potential dielectric material for dynamic random access memory and high k dielectric gate applications.     

体积应变对立方钛酸铅电子结构和光学性质的影响

本文利用第一性原理方法计算并分析了体积应变(-11%~11%)对立方顺电相PbTiO₃的结构、稳定性、电子结构和光学性质的影响。研究发现体积应变后PbTiO₃形成焓增大,稳定性下降,其中压应变对其稳定性的影响比拉应变大。当受到拉伸应变时,立方PbTiO₃由直接带隙半导体变为间接带隙半导体,且带隙随应变增大呈先增大后降低的趋势。在发生压应变时,从复介电函数、复折射率及吸收系数的分析结果可知,在自然光照下PbTiO₃的光吸收能力仅在个别波段有所增大,但总体呈减弱趋势,当产生拉伸应变时,介电峰、吸收峰红移,表明PbTiO₃在可见光范围内光吸收能力增强,并且当应变增大到11%时,PbTiO₃的吸收能力远高于本征立方相。     

Phase Transitions in Chlorobenzene-Cis-Decalin Mixtures: A Nuclear Magnetic Resonance,Thermal Analysis and Phase Diagram Study

Using nuclear magnetic resonance and differential scanning calorimetry we have been able to observe the molecular rotation properties of chlorobenzene-cis-decalin mixtures in their glassy, amorphous and crystalline phases. The results indicate: that in “rapidly” cooled samples the behavior of the host dominates the properties of the mixtures; that reorientation of the guest molecule is less restricted in the amorphous phase than in the glassy phase; that when the material crystallizes from the amorphous phase on warming, reorientation again becomes severely restricted. The temperatures at which these phenomena occur agree with the phase diagram that has been determined for these materials. Similar experiments on t butyl chloride-cis-decalin mixtures support the above conclusions. These conclusions are in agreement with the previous dielectric studies.

Our magnetic resonance and thermal analysis experiments support the argument that the behavior of the CD host dominates the behavior of guest polar molecules in rapidly cooled mixtures. At the lowest temperature (110 K) CD forms a glassy phase unaccompanied by any heat of crystallization. On warming this glassy phase transforms near 150 K to an amorphous phase where considerable motion of both host and guest molecules occurs. Above 160 K the material crystallizes and reorientation is once again severely restricted up to the eutectic melting of 210 K. There appears to be no time dependence to these transformations and, as long as one stays below the crystallization temperature, the glassy-amorphous transition is reversible.     

Structure and properties of epoxy/polyaniline nanocomposites

Epoxy/polyaniline nanocomposites have been prepared by in situ polymerization of aniline carried out in hydrophilic epoxy networks based on polyoxyethylene (POE) swollen in aqueous solutions of aniline hydrochloride. Formation of polyaniline (PANI) nanoparticles in water-rich phase of swollen networks has been revealed by transmission electron microscopy and infrared spectroscopy. The nanoparticles are dispersed in elastomeric matrix, suppress effectively crystallization of POE and increase glass transition temperature of the matrix.     

Internal bias field in TGS crystals doped with different impurities

The influence of an internal bias field formed by impurity ions of heavy metals and alpha-alanine molecules on the dielectric nonlinearity and emission properties of ferroelectric triglycine sulfate crystals has been studied. It is shown that a role of defects increases near the phase transition, which manifests itself in a decrease in the maximum values of the effective permittivity and an increase in the emission current with increasing impurity concentration.     

Structure and properties of self-assembled fluorocarbon–silica nanocomposites

The formation of fluorocarbon–silica nanocomposites by the self-assembly of a fluorinated surfactant and aminoalkoxysilane coupling agents was studied by X-ray diffraction, electron microscopy, NMR spectroscopy and thermal analysis. The prepared materials posses a lamellar nanostructure consisting of non-crystalline fluorinated and condensed silica layers, the latter being very thin. The prepared materials show interesting properties for applications, such as hydrophobicity, thermal stability, high content of aminopropyl groups and low dielectric constant (≈2.8), which is almost independent on frequency. Moreover, the dielectric response can be interpreted in the framework of the Maxwell–Wagner model.     

Nb2O5/Co2O3加入量对(Ba,Sr)TiO3基电容器陶瓷介电性能的影响

研究了Nb2O5/Co2O3加入量[质量分数,Nb/Co(摩尔比)=0.8]不同对(Ba,Sr)TiO3(Barium strontiumtitanate,BST)铁电电容器陶瓷介电性能的影响,得到不同Nb2O5/Co2O3加入量与BST陶瓷性能的关系。借助扫描电镜(SEM)和X射线衍射仪(XRD)研究不同Nb2O5/Co2O3加入量对BST陶瓷显微结构和物相的影响,探讨了Nb2O5/Co2O3加入量对BST陶瓷性能影响机理。结果表明:当Nb2O5/Co2O3加入量为1.0%时,可得到满足Y5V特性、介电常数为3934、介质损耗为2.6%综合性能好的BST陶瓷。Nb2O5/Co2O3加入量对BST陶瓷性能的影响是通过细晶化、压抑展宽居里峰、改善介电常数温度特性、减少介电常数、形成杂相、形成“晶核-晶壳”结构等进行。     

Conductivity and dielectric properties of polymer electrolytes PEO:LiN(CF3SO2)2 near glass transition

Results of measurements of PEO:LiN(CF₃SO₂)₂ polymer electrolytes of composition between 12:1 and 1.5:1 EO:Li, performed by impedance spectroscopy, impedance spectroscopy simultaneous with microscope observation, differential scanning calorimetry and X-ray diffraction were analyzed focusing on electrical properties of semicrystalline and rapidly cooled amorphous samples. In the loss spectra measured at low temperature, the occurrence of two dielectric relaxations was evidenced: local (β) and segmental (α). For each of the investigated electrolytes, the temperature dependence of the ionic conductivity and the frequency of α relaxation could be described by the VTF function with the same value of parameter T₀, which indicated close coupling of both phenomena. The local (β) relaxation exhibited an Arrhenius type temperature dependence. With increasing amount of salt, two effects were observed for amorphous samples: an increase of the glass transition temperature T_g affecting the α relaxation and changes of structure of PEO:LiN(CF₃SO₂)₂ complexes reflected in shift of the β relaxation frequency. Crystallization caused decrease of both the ionic conductivity and the strength of dielectric relaxations. The presence of crystalline phase was also reflected in a shift of the T_g of amorphous phase remaining in the system with respect to the T_g of amorphous electrolyte obtained by rapid cooling.     

Dielectric Properties of Diphasic Composites of BaTiO3 and LiFe5O8

A composite material has been prepared by sintering a mixture of a piezoelectric BaTiO₃ and a piezomagnetic ferrite phase. The two-phase nature of the composite has been characterised by X-ray analysis. The electrical resistivity and dielectric properties of the composite material are studied as a function of the volume fraction of the components. The effect of poling on the dielectric constant is also discussed.