Effects of BiMO3 on dielectric,ferroelectric, and piezoelectric properties of perovskite lead‐free piezoelectric BaTiO3–(Bi0.5Na0.5)TiO3 ceramics

New lead‐free piezoelectric ceramics of 0.9BaTiO₃–(0.1?x)(Bi_0.5Na_0.5)TiO₃–xBiMO₃, M=Al and Ga, where x=0.00‐0.10, were fabricated by the solid‐state reaction technique. The effect of BiMO₃ contents on the perovskite structure, phase transition, and dielectric, ferroelectric, and piezoelectric properties was investigated. X‐ray diffraction patterns showed that the ceramics exhibit a monophasic perovskite phase up to x=0.06, suggesting stabilized perovskite structures with B‐site aliovalent substitutions. Compositional‐dependent phase transitions were observed from tetragonal to pseudo‐cubic phase with increasing BiMO₃ amounts. Al³⁺ ions were found to stabilize the transition temperature of the ceramics, while significantly decreasing transition temperature, and a change in the dielectric peak were found with an increasing amount of Ga³⁺. Regarding Al³⁺ substitution, the remanent polarization (P_r) values were found to decrease slightly with the Al³⁺ amount. With regard to Ga³⁺ substitution, P_r values decreased with the Ga³⁺ amount up to 0.06 and then increased slightly. The ceramics became softer with a higher degree of substitution according to the lower coercive field (E_c), when compared with 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃ ceramics. Ceramics with a lower degree of substitution and tetragonal phase showed butterfly strain loops that correlated with normal ferroelectric behavior.     

Rheology of polymeric solutions I. Zero shear conditions

Based on kinetic considerations, the following equation, connecting the zero‐shear viscosity of polymeric solutions with temperature and the molecular weight and concentration of the polymer was derived: RTln η_R = KBφMⁿ /(1 + BφMⁿ), where η_R is relative viscosity (i.e., the ratio of the solution viscosity to the solvent viscosity); K represents a change in enthalpy of viscous flow from a pure solvent to a pure polymer at the same temperature or from a polymer of low molecular weight (M) to one of higher molecular weight, and has the dimensions of energy (e.g., J/mol) because the ratio BφMⁿ/(1 + BφMⁿ) is dimensionless; φ is the volume or molar fraction of a polymer in solution (concentration units can be used in dilute solutions); B is a constant related to the stiffness of the chains of the polymer in a given solvent; and at BφMⁿ >> 1, ln η_R = K/RT. The equation describes published data on the zero‐shear viscosity of four polar and nonpolar polymers in nine solvents with R² > 0.98. This approach allows the use of solutions of moderate concentrations for the characterization of polymers and opens a way for a single‐point degree of polymerization (DP) determination of polymers at moderate concentrations if constants K, B, and n of the equation are known. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2064–2073, 2002     

Detection of low levels of long‐chain branching in polydisperse polyethylene materials

Creep experiments have been applied to probe the zero‐shear viscosity, η₀, of polyethylene chains directly and precisely in a constant‐stress rheometer at 190°C. Such experiments, when combined with precise measurements of the weight‐average molecular weight, M_w, calibrated relative to linear chains of high‐density polyethylene, are shown to provide a very sensitive approach to detect low levels (0.005 branches per 1000 carbons) of long‐chain branching (LCB). This detection limit is shown to be insensitive to whether the molecular weight distribution (MWD) breadth, M_w/M_n, rises from about two to ten. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheology of a cellulose graft copolymer. Comparison with other closely packed gel thickeners

Hydrolyzed cellulose–polyacrylonitrile graft copolymer is a polyelectrolyte gel suspension with a high viscosity in water. It is a closely packed swollen gel particle suspension in the appropriate concentration range and has similar rheological properties to other thickeners of this type. Viscosities η in either water or salt solution are reduced to a single master curve by use of the reduced viscosity function η/cQ, where c is weight fraction of polymer and Q is swelling volume in excess solvent of the same ionic strength. The effective molecular weight between crosslinks, M_c, determined from shear modulus, corresponds to M_c values for other closely packed gel thickners of similar η/cQ. Among all examples of this class of thickener, the plateau values of η/cQ, which occur at cQ > 2, are approximately inversely proportional to M_c.     

Rheological behavior of pH‐responsive associating ionic polymers of diallyammonium salts and sulfur dioxide

In this study, the viscoelastic behavior of hydrophobically modified polyelectrolytes obtained from the hydrolysis of cationic acid salts (CAS's) as a function of their zwitterion fraction (x) and anion fraction (z) was studied. The dynamic viscosity (η′) dependence on frequency of polymer solutions of polybetaine/anionic polyelectrolyte (APE) with various compositions of x and z in 0.1N NaCl showed typical shear thinning behavior. η′ of a solution of CAS 4 (M₂‐4 (4 mol % hydrophobe)) attained a maximum value in the presence of 1.67 equiv of NaOH (corresponding to an x : z ratio of 33 : 67) and decreased with any further addition of NaOH. We suggest this maximum to be a result of a combined effect of coil expansion and hydrophobic association. The influence of the temperature and concentration on η′ of CAS 4 (M₂‐4) treated with 1.67 equiv of NaOH was also investigated. The rheology of CAS 4 (M₂‐4) samples treated with 1.67, 1.81, and 2.0 equiv of NaOH suggested a reversible network. However, for APE 7 (M₂‐5 (5 mol % hydrophobe)), elastic behavior was dominant, and the formation of highly interconnected three‐dimensional networks was suggested. At lower x : z ratios, the effect of coil expansion due to a higher APE fraction was more than counterbalanced by the lower degree of intermolecular hydrophobic associations, whereas at higher x : z ratios, coil contraction became the predominant effect. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of Bi0.5Na0.5HfO3 addition on the phase structure and piezoelectric properties of (K,Na)NbO3‐based ceramics

Lead‐free perovskite (1‐x)(K_0.48Na_0.48Li_0.04)Nb_0.95Sb_0.05O₃‐x(Bi_0.5Na_0.5)HfO₃ piezoelectric ceramics were prepared by a traditional ceramic fabrication method. An investigation was conducted to assess the effects of (Bi_0.5Na_0.5)HfO₃ content on the crystal structure, microstructure, phase‐transition temperatures, and piezoelectric properties of the ceramics. The X‐ray diffraction results, combined with the temperature dependence of dielectric properties, revealed that the ceramics experienced a structural transition from an orthorhombic phase to a tetragonal phase with the addition of (Bi_0.5Na_0.5)HfO₃, and a coexistence of orthorhombic and tetragonal phases was identified in the composition range of 0.005≤x≤0.015. An obviously improved piezoelectric activity was obtained for the ceramics with compositions near the orthorhombic‐tetragonal phase boundary, among which the composition x=0.005 exhibited the maximum values of piezoelectric constant d₃₃, and planar and thickness electromechanical coupling coefficients (k_p and k_t) of 246 pC/N, 0.435, and 0.554, respectively. Furthermore, the Curie temperature of the ceramics was found decreasing with the increase in (Bi_0.5Na_0.5)HfO₃ content, but still maintaining above 300°C for the phase boundary compositions. These results indicate that the ceramics are promising lead‐free candidate materials for piezoelectric applications.     

Composition‐ and Temperature‐Dependent Large Strain in (1−x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 Ceramics

Ternary solid solutions of (1 ? x)(0.8Bi_0.5Na_0.5TiO₃–0.2Bi_0.5K_0.5TiO₃)– xNaNbO₃ (BNKT–xNN) lead‐free piezoceramics were fabricated using a conventional solid‐state reaction method. Pure BNKT composition exhibited an electric‐field‐induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric‐to‐relaxor temperature T_F‐R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic‐to‐ergodic relaxor transition was presented, which featured the pinched‐shape polarization and sprout‐shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT–0.04NN, and the large strain was attributed to the reversible electric‐field‐induced transition between ergodic relaxor and ferroelectric phase.     

Viscoelastic properties of poly(ethylene-co-styrene) copolymers

The viscoelastic properties of narrowly distributed linear poly(ethylene-co-styrene) copolymers with different mole fractions of styrene (x_S = 0–20.5 mol %) and molecular weights (M_w = 64–214 kg/mol) were analyzed in the molten state at different temperatures by means of oscillatory rheometry. Analyzing the thermorheological properties of the polymers, we found that the time temperature superposition principle is fulfilled. The corresponding shift factors follow up to 16.5 mol % of styrene units the Arrhenius behavior of neat polyethylene. For a styrene content of about 20 mol %, the polymers no longer crystallize and a transition from Arrhenius to WLF behavior of pure polystyrene was observed. The zero shear viscosity, η₀, of the polymers was derived from the mastercurves. The determination of the plateau modulus by the well-known tan δ-min criterion is not possible due to the beginning crystallization in the corresponding temperature range. An approximate calculation of this value is based on the characteristic relaxation time λ_x = 1/ω_x, corresponding to the crossover of G′ and G′. Indeed, the characteristic modulus G_px calculated as η₀/λ_x is a good approximation for the plateau modulus G_p. The viscosity–molecular weight and relaxation time–molecular weight scaling relations were established for three copolymers with different molecular weights and nearly the same styrene content. For both material parameters, the scaling exponent is around 3.4, confirming the linear architecture of the investigated polymers. The mixing rules describing the change of such material parameters like zero shear viscosity or plateau modulus independent of styrene content are of logarithmic linear character using the weight fraction of styrene units instead of the mole fraction. The relations found allow the prediction of melt state properties for polymers with arbitrary styrene content. In the future, when catalysts with sufficient activity for the synthesis of high styrene content copolymers are available, these predictions will have to be checked. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:209–215, 1997     

Mathematical expressions for calculation of oil‐polymer blends

A study of the recent literature emphasized the importance of blending polymers with oils for improving the performance characteristics (like flexibility, corrosion resistance, etc.) of adhesives, coatings and laminates. Investigation of the available data revealed that several properties of such oil‐polymer blends could be correlated by molar refraction (R_M), with reasonable accuracies. The properties of the linseed oil‐polystyrene (PS) and linseed oil‐polymethyl methacrylate (PMMA) blends studied are iodine value (IV), hydroxyl value (HV), inherent viscosity (η), melting temperature (T_M), and glass transition temperature (T_g). In the case of safflower, palm and peanut oil‐sucrose polyester formulations, the viscosity at 40 °C (η₄₀) and the melting point T_M have been correlated by R_M with the average absolute deviations (ē) of 17.8% and 3.0%, respectively. Using the orientation polarization P_O (to represent polarity) in addition to R_M, η₄₀ and T_M of oil‐polyester formulations could be calculated with ē values of 8.9% and 1.7%, compared to 17.8% and 3.0% using R_M alone. The results indicated the importance of P_O in improving the accuracy of predictions for properties.     

Physical properties of PLGA films during polymer degradation

The rates of change of polymer properties (glass transition temperature, weight fraction sorbed water, and polymer molecular weight) were determined in poly (DL ‐lactide‐co‐glycolide) films under accelerated storage conditions. Films were stored at 70°C and 95%, 75%, 60%, 45%, or 28% relative humidity. Weight fraction sorbed water was determined by thermogravimetric analysis, the glass transition temperature (Tg_mix) of the polymer/water mixture by modulated temperature differential scanning calorimetry, and PLGA number‐average molecular weight (M_n) by size exclusion chromatography (SEC). Rates of moisture increase and Tg_mix decrease were related to the decrease in PLGA M_n through a modification of the Gordon‐Taylor equation. Understanding the relative rates of polymer physical and chemical degradation will allow for improved design of PLGA formulations that control rates of drug delivery and preserve drug stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dielectric and Raman Spectroscopic Studies of Na0.5Bi0.5TiO3–BaSnO3 Ferroelectric System

A series of lead‐free perovskite solid solutions of (1 ? x) Na_0.5Bi_0.5TiO₃(NBT)—x BaSnO₃(BSN), for 0.0 ≤ x ≤ 0.15 have been synthesized using a high‐temperature solid‐state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature (T_FR) and the temperature corresponding to maximum dielectric permittivity (T_m) are estimated from the temperature‐dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x. The disappearance of x‐dependence of A₁ mode frequency at ~134 cm^?1 for x ≥ 0.1 is consistent with rhombohedral‐orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral (x < 0.1)/orthorhombic (x ≥ 0.1) to tetragonal transition.     

Composition‐Controlled Synthesis of Bismuth Vanadate Photocatalysts via a Facile Electrochemical Method

Bismuth vanadate compounds including BiVO₄, Bi₂₅VO₄₀, and the composite Bi₂₅VO₄₀/Bi₇V₁₁O₉ with photocatalytic properties were firstly synthesized via a facile electrochemical strategy. The amount of NaOH in the electrolyte and electric currents were discovered to be crucial variables to the composition, morphology, and crystallinity of the products. Monoclinic phase BiVO₄ and Bi₂₅VO₄₀ with sillenite structure can be obtained at 2 A with NaOH concentration of 0–10^?4 and 0.1–0.4M, respectively. The acquirement of Bi₂₅VO₄₀/Bi₇V₁₁O₉ can be achieved with electric current 3–5 A in an electrolyte containing 0.4M NaOH. All the electrosynthesized samples exhibit good visible‐light‐driven photocatalytic activity in the degradation of rhodamine B, much higher than that of the commercial TiO₂ (P25).     

Lattice Dynamics,Dielectric Constants,and Phase Diagram of Bismuth Layered Ferroelectric Bi3Ti1−xWxNbO9+δ Ceramics

Lattice dynamics and phase transitions of Aurivillius ferroelectric Bi₃Ti_1?xW_xNbO_9+δ (BTWN100x, 0 ≤ x ≤ 15%) ceramics have been investigated by temperature‐dependent Raman spectra (80–800 K) and far‐infrared (FIR) reflectance spectra (6–300 K). The frequency, intensity, and line width of phonon modes as well as complex dielectric functions of BTWN100x ceramics have been extracted by fitting Raman and FIR reflectance spectra with the multi‐Lorentzian oscillator model. It was found that the dielectric constants at a certain frequency region become lower with increasing W compositions at room temperature due to the compressive stress on W–O bands. Moreover, the temperature‐dependent behavior of optical phonon modes in BTWN100x ceramics indicates that there are two intermediate phases during the phase transition from paraelectric I4/mmm to ferroelectric A2₁am phase on cooling. The phase diagram of BTWN100x ceramics as a function of W composition has been improved.     

Field cycling-induced evolution of functional properties in bismuth samarium ferrite ceramics

The field-controlled phase transition is a promising concept for the design of novel multiferroic materials. Rare-earth samarium-modified bismuth ferrite (Bi_1−xSm_xFeO₃) possesses a morphotropic phase boundary (MPB) that has similar free energies between the polar and nonpolar phases, making it an exceptional candidate. In this study, we investigated the electric field cycling-dependent behavior of ferroelectricity in Bi_1−xSm_xFeO₃ ceramics near MPB. During electric field cycling, a significantly enhanced remanent polarization was observed. Cycled Bi_0.86Sm_0.14FeO₃ and Bi_0.84Sm_0.16FeO₃ exhibited enhanced ferroelectric (remanent polarization >30 μC/cm²) and magnetic (remanent magnetization >0.20 emu/g) properties at room temperature. Through a systematic study of dynamic hysteresis measurements and a structural analysis, these results were attributed to a field cycling-induced nonpolar-to-polar phase transition. In situ high temperature measurements showed a previously unreported sharp anomaly of the piezoelectric coefficient (d₃₃) near the magnetic transition point (T_N). These results indicated a strong magnetoelectric coupling in rare earth-modified bismuth ferrite materials, suggesting the possibility of magnetically modulated piezoelectricity.     

Molecular structure of metallocene catalyst Cptt2ZrCl2 and structural analysis of PE catalyzed by Cptt2ZrCl2

Cp^tt₂ZrCl₂ (Cp^tt = η⁵?^tBu₂C₅H₃) was synthesized by the reaction of LiCp^tt with ZrCl₄ and characterized by X‐ray crystallographic studies. It was used as catalyst for ethylene polymerization. Structural analysis was carried out on the polyethylene (PE) catalyzed by Cp^tt₂ZrCl₂ via wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS). The degree of crystallinity (W_c,x) was calculated by WAXD. The semiaxises of the particles (a, a, b) of PE were determined by SAXS and it could be found that the crystalline particles of PE are mainly rod shaped determined by the characteristic function v₀ (r). The radius of gyration R_g, crystalline thickness L_c, the thickness of noncrystalline region L_a, long period L, electron‐density difference between the crystalline and noncrystalline regions η_c ? η_a, and the invariant Q are determined by SAXS. The results also indicate that a transition zone exists between the traditional “two phases” with a clear dimension of 1.3 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 169–175, 2005     

Enhanced ferroelectric and ferromagnetic properties of BiFeO3-PbTiO3 multiferroic solid solutions with Ba substitutions

Dense 0.6(Bi_0.9La_0.1)(Ga_0.05Fe_0.95)O₃-0.4(Pb_1-xBa_x)TiO₃ (BLGF-PBT, x = 0, 0.1, 0.2, 0.3, and 0.4) ceramics with different Ba contents were prepared by the solid-state reaction method, and effects of Ba contents on the structure and multiferroic properties were investigated. X-ray diffraction results indicate that the Ba-modified BLGF-PBT ceramics exhibit single perovskite structure without detectable secondary phases, and a transition from tetragonal phase to rhombohedral one takes place with the increase of Ba content. The piezoelectric constant d₃₃, remanent polarization P_r, and remanent magnetization M_r are improved by the Ba substitution simultaneously. Values of P_r, M_r, and d₃₃ of BLGF-PBT ceramics for the composition of x = 0.3 with the coexistence of tetragonal and rhombohedral phases are 20 μC/cm², 0.05 emu/g, and 256 pC/N, respectively, much higher than those without Ba modification. The significantly improved d₃₃ and M_r indicate that BLGF-PBT ceramics with Ba modification provide alternative materials for multifunctional devices.     

Optical Energy Storage Properties of (Ca1−xSrx)2Si5N8: Eu2+, Tm3+ Solid Solutions

While the reddish‐orange emitting phosphors M₂Si₅N₈:Eu²⁺(M = Ca, Sr) have been intensively investigated as potential materials for white‐light‐emitting diodes, in this study, optical energy storage properties of (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ (x = 0–1) solid solutions were tuned by cation substitution, which was commonly used to tune color point for improving w‐LEDs. Partial substitution of either Ca by Sr or Sr by Ca resulted in a redshifted Eu²⁺ emission which had a demarcation point at x = 0.5. Furthermore, the (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ materials exhibited similar persistent‐ and photostimulated luminescence behaviors with a maximum intensity at about x = 0.2. Such optical energy storage characters of the samples were attributed to the more appropriate trap depths (322–333 K) and higher density of energy level traps indicated by the thermoluminescence analysis.     

Photoluminescence,Structural, and Electrical Properties of Erbium‐Doped Na0.5Bi4.5Ti4O15 Ferroelectric Ceramics

Structural, electrical, and up‐conversion (UC) properties of Na_0.5Bi_4.5‐xEr_xTi₄O₁₅ (NBT–xEr³⁺) (0.00 < x < 0.40) ceramics have been studied. All the ceramic samples possessed a single‐phase orthorhombic structure. The unit cell volume, the lattice parameters a, b, and c, and orthorhombic distortion analyzed on the basis of Rietveld refinement were observed to decrease with increasing Er³⁺ contents (x). The average values of grain size were found to slightly decrease with increasing x. Raman spectroscopy revealed that (Bi₂O₂)²⁺ layers remained unaffected in the modified compositions, and Er³⁺ substitution for Bi³⁺ occurred predominantly at the A‐site in the perovskite blocks causing the cationic disorder and a slight decrease in the TiO₆ octahedral distortion. NBT–xEr³⁺ ceramic with x = 0.20 achieved the optimized photoluminescence. The relative intensity of green and red UC emissions could be tuned by changing Er³⁺ ions concentrations. Ferroelectric measurements revealed that Er³⁺ doping led to reduction in 2P_r and 2E_c. However, dielectric measurements showed that the incorporation of Er³⁺ ions increased T_c with simultaneously lowered tanδ at high temperature, implying that this ceramics can be suitable for high‐temperature sensor applications.     

Electrical Properties and Relaxor Phase Evolution of Li‐Modified BNT‐BKT‐BT Lead‐Free Ceramics

By conventional ceramics sintering technique, the lead‐free 0.85Bi_0.5Na_0.5(1?x)Li_0.5xTiO₃‐0.11Bi_0.5K_0.5TiO₃‐0.04BaTiO₃ (x =0–0.15) piezoelectric ceramics were obtained and the effects of Li dopant on the piezoelectric, dielectric, and ferroelectric properties were studied. With increasing Li addition, the temperature‐dependent permittivity exhibited the normal ferroelectric‐to‐ergodic relaxor (FE‐to‐ER) transition temperature (T_FE‐ER, abbreviated as T_F‐R) decreasing down to room temperature. The increasing Li content also enhanced the diffuseness of the FE‐to‐ER transition behavior. For composition with x = 0.15, a large unipolar strain of 0.37% ( = S_max/E_max = 570 pm/V) was achieved under 6.5 kV/mm applied electric field at room temperature. Both unipolar and bipolar strain curves related to the temperature closely, and when the temperature reached the T_F‐R, the normalized strain achieved a maximum value (e.g., for x = 0.10, = 755 pm/V) owing to the electric‐field‐induced ER‐to‐FE state transition.     

Large Strain Response in 0.99(Bi0.5Na0.4K0.1)TiO3–0.01(KxNa1−x)NbO3 Lead‐Free Ceramics Induced by the Change of K/Na Ratio in (KxNa1−x)NbO3

Influence of K/Na ratio in (K_xNa_1?x)NbO₃ on the ferroelectric stability and consequent changes in the electrical properties of 0.99(Bi_0.5Na_0.4K_0.1)TiO₃–0.01(K_xNa_1?x)NbO₃ (BNKT–K_xNN) ceramics were investigated. Results showed that change of K/Na ratio in KNN induces a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long‐range ferroelectric order, and correspondingly adjusts the ferroelectric–relaxor transition point T_F?R to room temperature. Accordingly, giant strain of ~0.46% (corresponding to a large signal d₃₃* of ~575 pm/V) which is comparable to that of Pb‐based antiferroelectrics is obtained at a K/Na ratio of ~1, and the emergence of large strain response induced by the change of K/Na ratio of KNN can be well explained by the correlation between the position of ferroelectric–ergodic relaxor phase boundary in the BNKT–K_xNN system and the tolerance factor t of the end number (K_xNN). In situ high‐energy X‐ray scattering experiments with external field reveals that the large strain response in the studied system is likely related to the electric field‐induced distortion from the pseudocubic structure.