Microwave-assisted sintering and improved dielectric,ferroelectric properties of 0.5[(Ba0.7Ca0.3)TiO3]–0.5[Ba(Zr0.2Ti0.8)O3] lead-free ceramics

0.5[(Ba_0.7Ca_0.3)TiO₃]–0.5[Ba(Zr_0.2Ti_0.8)O₃] lead-free ceramics were synthesised by coprecipitation method and sintered by fast microwave sintering (MWS) and by conventional sintering (CS) at 1200°C. After being sintered with the two different methods, the materials were characterised for structural, microstructural, frequency and temperature-dependent dielectric properties, Raman spectroscopy, and ferroelectric measurements. Results are compared and discussed in the present paper. X-ray diffraction confirms the presence of the tetragonal and rhombohedral phases in the composites sintered by both methods. The ferroelectric to paraelectric transition temperature (Tc) is increased in microwave-sintered composite. Diffuse constant (γ) values show BCT–BZT ceramics to be neither normal ferroelectrics nor relaxor ferroelectrics. Raman spectra confirm phase transition in the ceramic samples. Saturation polarisation (Ps) values are 7.62 and 4.28?µC?cm^?2 and nearly equal remanant polarisation (Pr) values were observed for BCT–BZT composite sintered with MWS and CS, respectively.     

Facile synthesis,characterization and material properties of a novel poly(vinyl cinnamate)/ nickel oxide nanocomposite

A poly(vinyl cinnamate) (PVCin) composite was synthesized by a simple one step in situ polymerization of vinyl cinnamate with nickel oxide (NiO) nanoparticles. The structural, morphological and thermal properties of the nanocomposite were characterized using Fourier transform (FT)‐Raman, FT infrared (FTIR) and UV spectroscopies, X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), differential scanning calorimetry and vibrating sample magnetometry (VSM) measurements. FT‐Raman, FTIR and UV spectroscopy results revealed the characteristic absorption and shifts of peaks of the polymer matrix, the shifts being attributed to the interaction of NiO nanoparticles with the polymer chains. The structural and morphological analysis using XRD, HRTEM and FESEM showed the uniform arrangement of nanoparticles within the polymer chains. VSM showed the ferromagnetic nature of the composite with an increasing saturation of magnetism. The glass transition temperature (T_g) of the composite was higher than that of pure PVCin and T_g of the composite increased with increasing nanoparticle content. The electrical resistivity of the nanocomposite was studied from AC and DC conductivity measurements. AC and dielectric properties were markedly enhanced in the whole range of frequency due to the presence of NiO nanoparticles. DC conductivity of the nanocomposite was much higher than that of PVCin and the conductivity of the nanocomposite increased with increasing content of NiO nanoparticles. © 2016 Society of Chemical Industry     

Influence of cobalt and sintering temperature on structure and electrical properties of BaZr0.05Ti0.95O3 ceramics

Pure and Co-modified BaZr_0.05Ti_0.95O₃ ceramics were fabricated by the traditional solid state reaction technique. The influence of cobalt and sintering temperature on structure, dielectric, ferroelectric properties and diffuse phase transition of BZT ceramics were investigated systematically. 1300 °C was the optimal sintering temperature for BZT ceramics. The solid solubility limit of Co ions in BZT matrix was determined to be 0.4 mol%. The introduction of a moderate amount of Co ions was believed to benefit the microstructure development and make the grain size more uniform. Compared with undoped counterparts, 0.4 mol% Co-modified ceramics showed equivalent ferroelectric properties with a high remnant polarization (P_r=9.6 μC/cm²) and a low coercive field (E_c=0.21 kV/mm). Besides these, a relative high dielectric coefficient (ε_r=2030) and a low dielectric loss (tan δ=1.85%) were also obtained on this composition. The degree of diffuse phase transition was enhanced by the addition of Co ions. The related mechanism of the diffused phase transition behavior was discussed.     

Synthesis and characterization of polyaniline/NiO nanocomposite

Spherical nickel oxide (NiO) nanoparticles were prepared by using nickel chloride as precursor in the ethylene glycol as solvent and urea as precipitant. The X‐ray diffraction study showed that NiO has single‐phase cubic structure with average crystallite size of 35 nm. The prepared NiO nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline: NiO (12 : 1, 6 : 1, and 3 : 1) at 5°C using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulfonic acid, as surfactant and dopant under N₂ atmosphere. The synthesized composites have been characterized by means of X‐ray diffraction (XRD), thermogravimetric analysis, Fourier transform infrared (FTIR), scanning electron microscopy, TEM, and vibrating sample magnetometer for its structural, thermal, morphological, and magnetic investigation. The XRD and FTIR studies show that the NiO particles are in the composite. The room temperature conductivities of the synthesized PANI, PANI/NiO (12 : 1), (6 : 1), and (3 : 1) composites were found to be 3.26 × 10^?4, 1.88 × 10^?4, 1.5 × 10^?4, and 4.61 × 10^?4 S/cm, respectively. The coercivity (H_c) and remnant magnetization (M_r) of NiO, PANI/NiO NCs (12 : 1), (6 : 1), and (3 : 1) at 5 K was found to be 8.22 × 10^?2, 6.31 × 10^?2, 6.42 × 10^?2, 6.27 × 10^?2 T, and 6.64 × 10^?3, 1.83 × 10^?4, 3.07 × 10^?4, and 3.98 × 10^?4 emu/g, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of thermochemical properties of Al nanoparticle and NiO nanowire composites

Thermochemical properties and microstructures of the composite of Al nanoparticles and NiO nanowires were characterized. The nanowires were synthesized using a hydrothermal method and were mixed with these nanoparticles by sonication. Electron microscopic images of these composites showed dispersed NiO nanowires decorated with Al nanoparticles. Thermal analysis suggests the influence of NiO mass ratio was insignificant with regard to the onset temperature of the observed thermite reaction, although energy release values changed dramatically with varying NiO ratios. Reaction products from the fuel-rich composites were found to include elemental Al and Ni, Al₂O₃, and AlNi. The production of the AlNi phase, confirmed by an ab initio molecular dynamics simulation, was associated with the formation of some metallic liquid spheres from the thermite reaction.     

Relaxor Characteristics of the Phase Transformation in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 Perovskite Ceramics

The single‐phase solid solutions of the (1 ? x)BaTiO₃–(x)Bi(Zn_1/2Ti_1/2)O₃ (BT–BZT) where x = 0.02–0.15 were prepared to investigate dielectric properties. Crystal structure of samples was obtained by using an X‐ray diffraction technique and Raman spectroscopy. For compositions with x ≤ 0.08, the solid solutions exhibited clear tetragonal symmetry and transitioned to pseudocubic symmetry as the content of BZT increased. The dielectric response exhibited a sharp phase transition within the BT‐rich region and the composition 0.92BT–0.08BZT was characterized by the onset of relaxor characteristics. As the concentration of BZT increased, the phase transition exhibited broader and more diffuse behavior. The polarization as a function of electric field (P–E) of these solid solutions also exhibited the same trend. The BT‐rich compositions showed a normal ferroelectric P–E response with a decrease in loop area as the BZT content increased. The composition at x = 0.08 exhibited a pinched hysteresis loop and with further increase in BZT content, the P–E response was characterized by slim loops.     

Crystallization Behavior and Multiferroic Properties of Bi3.15Nd0.85Ti3O12/CoFe2O4 Powders Synthesized by Sol–Gel Method

Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)/CoFe₂O₄ (CFO) composite ceramic powders with embedded structures were successfully prepared by sol–gel processing. Their crystallization behavior was characterized by XRD, DTA, FT‐IR, and HRTEM. The magnetic and ferroelectric phases of these composite ceramic powders segregate during calcination. The CFO phase forms easily at ~300°C, thereafter the BNdT matrix phase nucleates with grain growth at the CFO grain boundaries at temperatures >500°C. The CFO phase acts as a heterogeneous nucleation point for formation of the ferroelectric BNdT phase. Furthermore, the 0.5BNdT–0.5CFO composite ceramic powders go through a ferroelectric–paraelectric phase transition at 259°C, and the magnetic CFO nanoparticles (50–100 nm, under calcination at 600°C) embedded in the ferroelectric matrix, show superior magnetic behavior (M_max = 16.50 emu/g), comparable to pure CFO nanoparticles.     

Preparation and characterization of new nanocomposite polymer films containing NiO nanofillers

Nanocomposite solid polymer films based on the poly(exo‐N‐phenyl‐7‐oxanorbornene‐5,6‐dicarboximide) (PPhONDI)/LiClO₄/NiO system have been designed, and the effect of inorganic NiO nanofiller in different amounts on the film properties has been examined. The exo‐PPhONDI/LiClO₄/NiO polymer system is the first solid nanocomposite polymer electrolyte film example based on a ring‐opening metathesis polymerization (ROMP) host polymer. The NiO nanoparticles were prepared by two‐step chemical syntheses, and the thermoplastic host polymer, exo‐PPhONDI, was synthesized via ROMP. Composite polymer films were prepared by the solution‐casting method. The amount of nanoparticles was varied from 1 to 15 wt % of NiO. The conductivity of the nanocomposite solid polymer systems was influenced by the NiO nanofiller concentration. The composite films based on exo‐PPhONDI ROMP polymer with the highest conductivity were achieved for the composition with 8 wt % of NiO nanofiller and 10 wt % of LiClO₄ dopant. The prepared films were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy (SEM). The SEM results showed that the filler was well distributed in the polymer matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45938.     

Dielectric properties and diffuse phase transition behavior of CuO-doped lead-free Ba(ZrxTi1−x)O3 ceramics

CuO-doped lead-free Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared through a solid state processing technique, and the effects of CuO on microstructure, dielectric properties and diffuse phase transition behavior were investigated. The average grain sizes were increased by CuO doping. The temperature and frequency dependences of the dielectric constant revealed that CuO-doped BZT20 ceramics exhibited broad diffuse phase transition behavior. The dielectric constant increased with increasing CuO concentration. The value of T_m and degree of diffusion (γ) changed regularly in the studied compositional ranges. The BZT20 samples with 1.0 mol% CuO doping, sintered at 1310 °C, showed excellent dielectric property and lower diffusivity with ε_m=21,371 and γ=1.87. These results can be explained by the disordered distribution of Cu ions in the B sites and the weakened bonding force with oxygen ions in Cu substituted BZT20 structure.     

FTIR and Raman Spectroscopy of Carbon Nanoparticles in SiO2, ZnO and NiO Matrices

Coatings of carbon nanoparticles dispersed in SiO₂, ZnO and NiO matrices on aluminium substrates have been fabricated by a sol–gel technique. Spectrophotometry was used to determine the solar absorptance and the thermal emittance of the composite coatings with a view to apply these as selective solar absorber surfaces in solar thermal collectors. Cross-sectional high resolution transmission electron microscopy (X-HRTEM) was used to study the fine structure of the samples. Raman spectroscopy was used to estimate the grain size and crystallite size of the carbon clusters of the composite coatings. X-HRTEM studies revealed a nanometric grain size for all types of samples. The C–SiO₂, C–ZnO and C–NiO coatings contained amorphous carbon nanoparticles embedded in nanocrystalline SiO₂, ZnO and NiO matrices, respectively. Selected area electron diffraction (SAED) showed that a small amount of Ni grains of 30 nm diameter also existed in the NiO matrix. The thermal emittances of the samples were 10% for C–SiO₂, 6% for the C–ZnO and 4% for the C–NiO samples. The solar absorptances were 95%, 71% and 84% for the C–SiO₂, C–ZnO and C–NiO samples, respectively. Based on these results, C–NiO samples proved to have the best solar selectivity behaviour followed by the C–ZnO, and last were the C–SiO₂ samples. Raman spectroscopy studies revealed that both the C–ZnO and C–NiO samples have grain sizes for the carbon clusters in the range 55–62 nm and a crystallite size of 6 nm.     

High magnetic and ferroelectric properties of BZT-LSM multiferroic composites at room temperature

In this research, the effects of La_0.7Sr_0.3MnO₃ additive on the phase evolution, microstructure, dielectric, ferroelectric and magnetic properties of BaZr_0.07Ti_0.93O₃ ceramics were systematically investigated. The (BaZr_0.07Ti_0.93O₃)/x(La_0.7Sr_0.3MnO₃) or BZT/xLSM (where x?=?0, 5, 10 and 20?mol%) ceramics were prepared via a solid state reaction method. A pure perovskite phase is observed for the samples of x?≤?10?mol%. The M-H hysteresis loops also show an improvement in the magnetic behavior for higher LSM content samples as well as the modified ferroelectric properties. However, the 5?mol% sample exhibited the optimum ferroelectric and ferromagnetic properties with remnant magnetization (M_r) and remanent polarization (P_r) of 2.38?emu/g and 10.5?µC/cm², respectively. The dielectric-temperature curves show that the two phase-transition temperatures as observed for the unmodified BZT ceramic merges into a single phase-transition temperature for the 5?mol% sample and then become flat curves for the 10?mol% sample. In addition, the mechanical properties i.e. Knoop hardness and Young's modulus values increase with increasing LSM content, where Knoop hardness and Young's modulus values for the 20?mol% sample are increased by ~ 45% and ~ 104%, respectively, as compared to the unmodified sample.     

Multiferroic (Nd,Fe)-doped PbTiO3 ceramics with coexistent ferroelectricity and magnetism at room temperature

We report the structural, dielectric, elastic, ferroelectric and ferromagnetic properties of multiferroic (Nd, Fe)-doped PbTiO3 perovskite ceramics with composition (Pb_0.88Nd_0.08)(Ti_0.94Fe_0.04Mn_0.02)O₃, prepared by different solid state reaction methods: the first one based on a single-stage calcination (Method I) and the second based on a double-stage calcination (Method II). Structural, dielectric and anelastic measurements evidenced a double phase transition for samples prepared by Method I, which has been attributed to phase separation. This phase separation has been confirmed also by TEM and HRTEM investigations. Samples prepared by Method II showed a single phase transition from paraelectric to ferroelectric phase. We found coexistent ferroelectric and ferromagnetic properties, also at room-temperature, but only for ceramics prepared by Method II. The crucial role of calcination process for avoiding phase separation and obtaining homogeneous structures with ferroelectric and ferromagnetic order is underlined.     

Electrical properties of lead-free 0.98(Na<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-0.02Ba(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by optimizing sintering temperature

Lead-free 0.98(Na_0.5K_0.5)NbO₃-0.02Ba(Zr_0.52Ti_0.48)O₃ [0.98NKN-0.02BZT] ceramics were fabricated by the conventional mixed oxide method with sintering temperature at 1,080°C to 1,120°C. The results indicate that the sintering temperature obviously influences the structural and electrical properties of the sample. For the 0.98NKN-0.02BZT ceramics sintered at 1,080°C to 1,120°C, the bulk density increased with increasing sintering temperature and showed a maximum value at a sintering temperature of 1,090°C. The dielectric constant, piezoelectric constant [d ₃₃], electromechanical coupling coefficient [k _p], and remnant polarization [P _r] increased with increasing sintering temperature, which might be related to the increase in the relative density. However, the samples would be deteriorated when they are sintered above the optimum temperature. High piezoelectric properties of d ₃₃ = 217 pC/N, k _p = 41%, dielectric constant = 1,951, and ferroelectric properties of P _r = 10.3 μC/cm² were obtained for the 0.98NKN-0.02BZT ceramics sintered at 1,090°C for 4 h.     

Structure and properties of Bi(Zn½Ti½)O3-modified Pb(Zr,Ti)O3 piezo-/ferroelectric ceramics around the ternary morphotropic phase boundary

To develop high-performance piezo-/ferroelectric materials, Bi(Zn_½Ti_½)O₃–PbZrO₃–PbTiO₃ (BZT–PZ–PT) ternary solid solution with compositions around the morphotropic phase boundary (MPB) is synthesized by solid-state reaction. The crystal structure and electric properties are investigated systematically by X-ray powder diffraction (XRD), dielectric spectroscopy, and ferroelectric and piezoelectric measurements. On the basis of the results of the XRD, dielectric and ferroelectric measurements, the pseudo-binary phase diagram of the yBi(Zn_½Ti_½)O₃–(1 − y)[(1 − x)PbZrO₃–xPbTiO₃] system has been constructed for three series, namely, y = 0.05, 0.10, and 0.15. It is found that the introduction of BZT into the PZT system makes the paraelectric to ferroelectric phase transition more diffuse, brings the MPB to a lower PT content, and enlarges the MPB region. The best properties with an improved dielectric constant ε' = 1248, and a large remnant polarization P_r = 33 μC/cm², as well as a relatively high T_C = 286°C, and a high coercive field E_c = 23 kV/cm was achieved in the y = 0.15 series with MPB composition x = 0.425, making it a promising material for high-power piezoelectric applications.     

Structural,dielectric and piezoelectric properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–Bi(Zn0.5Ti0.5)O3 thin films prepared by sol–gel method

Lead free (1−x)(0.8Bi_0.5Na_0.5Ti_0.5O₃–0.2Bi_0.5K_0.5TiO₃)–xBiZn_0.5Ti_0.5O₃ (x=0–0.06) (BNT–BKT–BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel processing technique. The effects of BZT content on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT–BKT–BZT thin films were investigated systematically. The BNT–BKT–BZT thin films undergo a transition from ferroelectric to relaxor phase with increasing temperature. The phase transition temperature decreases with the increase of BZT content. The BNT–BKT–BZT thin film with x=0.04 exhibits the best ferroelectric properties (P_max=40 µC/cm² and P_r=10 µC/cm²), largest dielectric constant (ε=560) and piezoelectric constant (d₃₃=40 pm/V). This finding demonstrates that the BNT–BKT–BZT thin film has an excellent potential for demanding high piezoelectric properties in lead free films.     

Phase formation and electrical properties of Ba(ZrxTi1−x)O3 ceramics synthesized through a novel combustion technique

High quality Ba(Zr_xTi_1?x)O₃ (BZT, 0.025≤x≤0.150, step=0.025) ceramic has been prepared by the combustion technique. The raw materials were mixed with CH₄N₂O and calcined at 1000 °C and sintered at 1375 °C. For Ba(Zr_xTi_1?x)O₃ with x=0.025, the ceramics exhibited orthorhombic structure at room temperature. The crystal structure was transformed to rhombohedral, tetragonal and cubic phase, respectively with increasing zirconium content. The effect of x on dielectric properties has been studied intensively. It is found that the phase formation, which was affected from zirconium substitution, strongly influences the dielectric behavior. The rhombohedral phase decreases the maximum dielectric constant while the tetragonal phase enhances it. An extrapolation studied revealed the phase transition peaks merged into one peak at x ～0.094. The highest diffuseness constant of 1.95 was observed in BZT with 0.075 mol% zirconium. This was caused by the broadest dielectric peak of ferroelectric phase transition and the imminent diffusion between ferroelectric phase transition peak and Curie phase transition peak. The ferroelectric properties were sensitive to the phase exhibited in BZT system.     

The effect of NiO addition on the grain boundary behavior and electrochemical performance of Gd-doped ceria solid electrolyte under different sintering conditions

It has been reported that some transition metal oxides are effective aids both for the densification and the grain boundary behavior of ceria-based electrolytes. In the present work, NiO which is the most popular component of the anode of solid oxide fuel cells was added directly into the electrolyte ceramic, Ce_0.8Gd_0.2O_1.9, to investigate the effects of the presence of NiO on the properties of GDC electrolyte. All of the samples possess a single phase with cubic fluorite structure. The grain size is increased by the addition of NiO when the sintering temperature is 1400 °C. This modification in chemical composition also results in a decrease in activation energy and thus a tendency to enhance grain boundary mobility. The maximum power density of the composite electrolyte single cell is higher than that of a GDC single cell. Therefore, NiO can be used as an effective aid for ceria-based electrolytes.     

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

The molecular mobility in copolymers of vinylidene fluoride–hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10^?1–10⁷ Hz), differential scanning calorimetry DSC (?100 to 150°C), and of wide angle X‐ray diffraction WAXS. Four relaxation processes and one ferroelectric‐paraelectric phase transition have been detected. The process of the local mobility β‐ (at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (α_a‐relaxation) depend on the ratio of comonomer with lower kinetic flexibility. α_c‐relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of α‐ (α_p‐) phase. Diffuse order–disorder relaxor type ferroelectric transition connected with the destruction of the domains in low‐perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (α‐process) was observed for both copolymers in high‐temperature region. DSC data shows that it falls on the broad temperature region of α‐phase crystals melting. It is considered to be connected with the space charge relaxation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of ZnO doping on structural,dielectric, ferroelectric and piezoelectric properties of BaZr0.1Ti0.9O3 ceramics

This study provides a fundamental understanding of structural, dielectric, ferroelectric and piezoelectric properties of bare and ZnO-doped BaZr_0.1Ti_0.9O₃ (BZT) solid solutions synthesized using mechanochemical activation technique. Structural investigation has been carried out using XRD patterns of the synthesized compositions by Rietveld refinement method. It confirms the formation of tetragonal phase with P4mm space group for ZnO doping up to 2.5 wt%, while in 5.0 wt% ZnO-doped sample, BZT and ZnO are distributed as individual phases of tetragonal (P4mm) and hexagonal (P6₃mc), respectively. Microstructural analysis shows that average grain size increases quite rapidly with the increase of ZnO content. Detailed analysis of dielectric constant as a function of temperature for the prepared samples shows that the frequency independent dielectric constant maximum shifts to lower temperature with increase in ZnO doping. The ferroelectric ordering is confirmed using P-E loop measurements. The piezoelectric constant of the synthesized specimens were found to decrease with increasing ZnO content.