Temperature Of Maximum Dielectric Constant Research Articles

Enhancement of energy-storage properties of K0.5Na0.5NbO3 modified Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 lead-free ceramics

A lead-free ceramics (1 − x)(0.84Na0.5Bi0.5TiO3–0.16K0.5Bi0.5TiO3)–xK0.5Na0.5NbO3 (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15) for energy-storage application have been fabricated by conventional solid state method. All compositions were crystallized into perovskite solid solution structure ascertained by XRD. SEM micrograph revealed that homogeneous grain could be obtained by addition of appropriate K0.5Na0.5NbO3 (KNN). The depolarization temperature (Td) decreased significantly from 140 to 70 °C, while the maximum dielectric constant temperature (Tm) reduced slightly with increasing KNN. And the addition of KNN improved the energy-storage properties significantly by weakening the ferroelectricity of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT–KBT) ceramics. When x = 0.09, the highest energy-storage density (W = 1.51 J/cm3) and energy efficiency (η = 65.0 %) were obtained at room temperature. Besides, the temperature stability of energy-storage density could satisfy ΔW/W100°C ≤ ±20 % when the addition of KNN was over 0.09 from 20 to 150 °C.

Enhanced Piezoelectric Properties of Lead-Free La and Nb Co-Modified Bi0.5(Na0.84K0.16)0.5TiO3-SrTiO3 Ceramics

New lead-free piezoelectric ceramics 0.96[{Bi0.5 (Na0.84 K0.16)0.5}1-xLax(Ti1-y Nby)O3]-0.04SrTiO3 (BNKT-ST-LN, where x = y = 0.00 ≤ (x = y) ≤ 0.015) were synthesized using the conventional solid-state reaction method. Their crystal structure, microstructure, and electrical properties were investigated as a function of the La and Nb (LN) content. The X-ray diffraction patterns revealed the formation of a single-phase perovskite structure for all the LN-modified BNKT-ST ceramics in this study. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves became more diffuse with an increasing LN content. At the optimum composition (LN 0.005), a maximum value of remnant polarization (33 C/cm2) with a relatively low coercive field (22 kV/cm) and high piezoelectric constant (215 pC/N) was observed. These results indicate that the LN co-modified BNKT-ST ceramic system is a promising candidate for lead-free piezoelectric materials.

Effect of Structural Modification by MnO2Addition on the Electrical Properties of Lead Free Flux Grown (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3Single Crystals

In this study, single crystals of 0.25 mol % Mn-modified lead-free (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3 grown by self-flux method are investigated. The crystal shows coexistence of tetragonal and cubic phases in the perovskite structure. EDAX analysis shows a uniform Mn doping for the BNKMT single crystals. The depolarization temperature (Td) and the temperature of dielectric constant maximum (Tm) are found to be 175 and 310 °C respectively. The complex impedance plot exhibited single impedance semicircle identified over the frequency range of 200 Hz to 2 MHz. The ac conductivity results indicate activation energies in the range of 0.035–0.040 eV at low temperatures and 0.1–0.5 eV at high temperatures. The piezoelectric charge coefficient d33 reaches a maximum of 202 pC/N. Nonswitchable ferroelectric hysteresis showing a strong anomaly along the polarization axis with temperature are observed. Fatigue-free behavior up to 10,000 electrical cycles is observed, making the crystals favorable for high precision sensors, capacitors, and actuator applications.

Structure and temperature dependent electrical properties of lead-free Bi0.5Na0.5TiO3- SrZrO3 ceramics

Lead-free SrZrO3-modified Bi0.5Na0.5TiO3 (BNT-SZ) ceramics were fabricated by a conventional solid state reaction method. X-ray diffraction analysis reveals a pure perovskite phase without any traces of secondary phases. Scanning electron microscopy images depicts dense grain morphology. The temperature dependences of the dielectric behavior was measured in the temperature range of 50-500 °C at 100 kHz. With the increase in SZ content, the dielectric constant (εr) constantly decreased and the maximum dielectric constant temperature (Tm) shifted towards lower temperatures. In addition to this, ferroelectric hysteresis loops indicated a disruption of ferroelectric order and increase in the relaxor character of BNT ceramics with increase in SZ concentration. A maximum values of remnant polarization (32 μC/cm2) and piezoelectric constant (100 pC/N) were observed at SZ5 and SZ4, respectively.

Enhanced ferroelectric order in Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramics by ZnO modification

In this research, the effects of ZnO modification on ferroelectric order of Pb (Mg1/3Nb2/3)0.9Ti0.1O3 (PMNT) ceramics were studied through characterizations of dielectric and ferroelectric properties. The PMNT/xZnO (where x = 0, 0.4, 2.0, 4.0 and 11.0 mol.%) ceramics were prepared by solid state reaction and sintering process. The lattice parameter a and unit cell volume of pure PMNT ceramic were increased with ZnO modification. The temperature of maximum dielectric constant (Tmax), the freezing temperature (Tf), the depolarization temperature (Td) and the polar ordering temperature (TP) increased while the diffuseness parameter (δ) decreased with the increase in ZnO content, indicating an enhancement of ferroelectric ordering and a decrease in a degree of relaxor behavior of PMNT ceramics by ZnO modification. Polarization-electric field hysteresis loop and butterfly-like strain-electric field curve were displayed around room temperature in the 11.0 mol.% ZnO-modified PMNT sample, which indicated an establishment of polar macro domains. Electrostrictive coefficient (M) reached a highest value of 22.22 × 10−16 m2/V2 for the PMNT/4.0 mol.%ZnO ceramic, which made it a promising material for applications as electrostrictive actuators.

Structure, photoluminescence and electrical properties of BaBi3.5Eu0.5Ti4O15 ceramics

Aurivillius phase BaBi3.5Eu0.5Ti4O15 (BBET) ceramics were synthesized using a solid state reaction method. X-ray diffraction analysis confirmed that the compound is a four-layer Aurivillius oxide with tetragonal space group I4/mmm and Raman spectrum indicated that Eu3+ ions occupy the A site. It was observed that the average grain size is 0.5–2.5μm by the scanning electron microscope. The photoluminescence spectra showed that the intense emission bands centered at about 593 and 615nm are due to the transitions of 5D0→7F1 and 5D0→7F2 of Eu3+ ions respectively. The temperature of dielectric constant maximum, the room temperature dielectric constant and loss at 1MHz are 373°C, 222 and 0.013, respectively. The activation energy of dielectric relaxation was estimated to be 1.17eV, which could be attributed to the thermal motion of oxygen vacancies. The BBET ceramics had a remnant polarization (2Pr) of 0.75μC/cm2 at room temperature. The results suggest that BBET ceramics can be considered as a promising multifunctional optoelectronic material.

Enhanced electric field-induced strain and ferroelectric behavior of (Bi0.5Na0.5)TiO3–BaTiO3–SrZrO3 lead-free ceramics

The crystal structure, electric field-induced strain (EFIS) and piezoelectric properties of lead-free SrZrO3-modified Bi0.5Na0.5TiO3–0.065BaTiO3 (BNBT–SZ100x, with x=0–10) ceramics were investigated. The X-ray diffraction analysis revealed a phase transformation from tetragonal to pseudocubic symmetry with increasing amounts of SZ. A large EFIS of 0.39% was obtained at the critical composition of BNBT–SZ2 which corresponds to a normalized strain (Smax/Emax) of 722pm/V at a low applied field of ~5.5kV/mm. Ferroelectric curves indicated a disruption of ferroelectric order and a decrease in the remnant polarization and coercive field. A maximum value of piezoelectric constant (197pC/N) and electromechanical coupling coefficient (29.4%) was obtained for SZ1 ceramics. The maximum dielectric constant temperature (Tm) and depolarization temperature (Td) shifted towards lower temperatures and curves became more diffuse with increasing amounts of SZ. The results indicate that BNBT–SZ100x ceramics can be promising candidates for lead-free actuators.

Lanthanum Dependence of the Electrically Controlled Light Scattering Performances of PLZT Transparent Ceramics

Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electrically controlled light scattering effects. By the hot-press sintering method, a series of PLZT (X/70/30) ceramics with different La concentration (7.3, 7.4, 7.45, 7.5, 7.6 mole %) have been synthesized to figure out its influence on the electrically controlled light scattering performances. XRD patterns reveal the formation of a single-phase perovskite structure for all samples. The PLZT (7.3/70/30, 7.4/70/30, 7.45/70/30) samples exhibit a ferroelectric behavior, but with the La concentration increasing, the samples exhibit a tendency of a double hysteresis loop which is due to antiferroelectric phase coexisted. The temperature of maximum dielectric constant (Tm) of the PLZT (X/70/30) ceramics shifts from ~99 °C to ~87 °C with the increasing of La concentration at 1 kHz. All samples exhibit a high transmittance (61%, 0.35 mm) within the wavelength range from visible to near-infrared light. Depending on the La concentration, the light scattering behavior of PLZT ceramics exhibit two main types, in which PLZT (7.45/70/30) promises a unique potential application in laser modulators for its outstanding advantages of less energy consumption and relatively larger contrast ratio.

Effect of SrZrO3substitution on structural and electrical properties of lead-free Bi0.5Na0.5TiO3-BaTiO3ceramics

In this study, a new lead-free ceramic system of (1–x)Bi0.5Na0.5TiO3–0.065BaTiO3–xSrZrO3 BNBT–SZ100x (with x = 0–0.10) was prepared by a conventional solid-state reaction method and its structural and electrical properties were studied. XRD analysis revealed the formation of pure perovskite phase for all ceramics. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves become more diffuse with increasing amount of SZ addition. The ferroelectric curves indicated a disruption of ferroelectric order upon SZ addition into BNBT ceramics. A maximum value of remnant polarization (30 µC cm−2), piezoelectric constant (197 pC N−1) and electromechanical coupling coefficient (29.4%) was observed for SZ1 ceramics.

Structural and electromechanical properties of lead-free Na0.5Bi0.5TiO3-BaZrO3ceramics

The effect of BaZrO3 (BZ) addition on the crystal structure, ferroelectric, and piezoelectric properties of Na0.5Bi0.5TiO3 (NBT) ceramics synthesized by a conventional solid-state reaction method was systemically investigated. The X-ray diffraction profile reveals the formation of single-phase perovskite structure for all BZ modified NBT ceramics in composition range (x = 0–0.08). With the increase in BZ content, the maximum dielectric constant (Tm) and depolarization temperature (Td) peaks shift towards lower temperatures. At room temperature, the ferroelectric response increase with increase in BZ concentration. A maximum value of remanent polarization (Pr) 30 µC/cm2 was obtained at x = 0.04 and, however, with further increase in BZ content polarizations values decrease. The piezoelectric constant (d33) increased from 60 pC/N for pure NBT to 112 pC/N for x = 0.040. Furthermore, a significant enhancement in the normalized strain ( = Smax/Emax = 500 pm/V) was observed at x = 0.055 which can be attributed to ferroelectric and relaxor ferroelectric phase transformation.

Unification of the negative electrocaloric effect in Bi1/2Na1/2TiO3-BaTiO3 solid solutions by Ba1/2Sr1/2TiO3 doping

The microscopic mechanisms of the negative electrocaloric effect (ECE) of the single-phase (1−x)(0.94Bi1/2Na1/2TiO3-0.06BaTiO3)-xBa1/2Sr1/2TiO3 (BNT-BT-BST) perovskite solid solutions fabricated via the sol-gel technique are explored in this study. Dielectric and mechanical relaxation analyses are employed to investigate the ferroelectric and structural transitions of the samples. The electrocaloric properties of the samples were measured by thermodynamics Maxwell relations. The difference between the depolarization temperature (Td) and the maximum dielectric constant temperature (Tm) was found to decrease with increasing BST content. Doping with BST stabilized the ferroelectric phase along with unifying the EC temperature changes (ΔT) to only negative values. The origin of the uniform negative ECE of BNT-BT-BST is discussed.

Structural and electrical properties of four-layers Aurivillius phase BaBi3.5Nd0.5Ti4O15 ceramics

A new compound of barium bismuth neodymium titanate BaBi3.5Nd0.5Ti4O15 was synthesized using the traditional solid-state reaction method. X-ray diffraction analysis confirmed the compound to be a layered tetragonal structure and Raman spectrum indicated that Nd ions occupy the A site. The plate-like morphology with average grain size about 2–4μm was observed by a scanning electron microscope (SEM). A precision impedance analyzer was used to measure the dielectric properties and impedance spectroscopy of the ceramics. The results show that the temperature of dielectric constant maximum (Tm), the room temperature dielectric constant (εr) and loss (tanδ) at 100kHz are 287°C, 326 and 0.017, respectively. The modified Curie–Weiss law was used to describe the relaxor behavior of the ceramics which was attributed to the A site cationic disorder. The remnant polarization (2Pr) of the sample was observed to be 1.27μC/cm2 at room temperature.

Enhancement in dielectric, ferroelectric, and electrostrictive properties of Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramics by CuO addition

Effects of CuO on dielectric, ferroelectric and electrostrictive properties of Pb(Mg1/3Nb2/3)0.9Ti0.1O3(PMNT) ceramics were studied. The PMNT/xCuO (with x=0, 0.2, 0.4, 2.0 and 4.0mol.%) ceramics were prepared by using solid state reaction and sintering process. It was found that the pseudo-cubic lattice parameter, a, gradually increased while the angle α decreased with increasing CuO content. Maximum dielectric constant showed a decreasing trend with increasing CuO with an abrupt increase in value at x=2.0mol.%. The temperature of maximum dielectric constant and depolarization temperature tended to increase while the diffuseness of dielectric peak decreased with increasing CuO concentration. Remanent polarization and coercive field of pure PMNT sample were ∼1.8μC/cm2 and 0.6kV/cm, respectively, which were increased to ∼3.5μC/cm2 and 1.8kV/cm when x=0.2mol.%. With x>0.2mol.%, coercive field gradually decreased with increasing CuO content while remanent polarization did not significantly change. With x⩽2.0mol.%, induced strain and electrostrictive coefficient tended to increase with increasing CuO content, with maximum values of 0.09% (at 10kV/cm) and 19.90×10−16m2/V2, respectively, for the PMNT/2.0mol.% CuO sample. An enhancement in polar order of PMNT ceramics due to an addition of CuO was observed.

Preparation and Properties of La and K Co-Doped BaTiO3 Lead-Free Piezoelectric Ceramics

Phase-pure perovskite structure (KxLa0.05-x)Ba0.95TiO3 ceramics were prepared by the conventional solid-state reaction method. With the increase of the ratio of K/La, crystal structure of the (KxLa0.05-x)Ba0.95TiO3 ceramics changes gradually from pseudo-cubic perovskite structure to tetragonal one. The sintered (KxLa0.05-x)Ba0.95TiO3 ceramics exhibit rather high relative density and rather homogenous microstructure morphology composed of submicron grains. With the decrease of the ratio of K/La, the temperature of dielectric constant maximum (TC or Tm) decreases almost linearly, and the dielectric response character of the (KxLa0.05-x)Ba0.95TiO3 ceramics changes from narrow and sharp dielectric peaks to broad and diffused ones gradually accompanied by the increase of dielectric frequency dispersion. The (KxLa0.05-x)Ba0.95TiO3 ceramics exhibit rather slim P-E hysteresis loops with slight character of asymmetry. Via adjusting the ratio of K/La, the acceptor and donor doping states are tailored, therefore, excellent ferroelectric and piezoelectric properties can be obtained in the (KxLa0.05-x)Ba0.95TiO3 ceramics.

Room temperature multiferroic Ba4Bi2Fe2Nb8O30: Structural, dielectric, and magnetic properties

A room temperature multiferroic compound Ba4Bi2Fe2Nb8O30 was synthesized using a solid state reaction technique. Rietveld analysis of x-ray diffraction data shows that Ba4Bi2Fe2Nb8O30 has a tetragonal (space group P4bm) tungsten bronze structure. In this structure, the Fe3+ and Nb5+ statistically occupy the octahedral center while the Ba2+ ions and the Bi3+ ions occupy the pentagonal channels and the square channels, respectively. Diffuse dielectric peaks with strong frequency dispersion in the temperature range from 150 to 300 K can be attributed to the random distribution of Fe3+ and Nb5+ at B sites. Magnetic hysteresis loop at room temperature is also obtained, which suggests that Ba4Bi2Fe2Nb8O30 is a room temperature multiferroic compound. The coupling between the relaxor behavior and magnetic ordering is verified by observing an increase of magnetization near the maximum dielectric constant temperature.

Effect of Annealing on the Structure and Dielectric Properties in PZT-PCoN Ceramics

he solid solution between the normal ferroelectric Pb(Zr1/2Ti1/2)O3 (PZT) and relaxor ferroelectric Pb(Co1/3Nb2/3)O3 (PCoN) was synthesized by the solid state reaction method. Sintered PZT-PCoN ceramics were annealed at temperatures ranging from 850 to 1,100°C for 4 h. X-ray diffraction patterns revealed changes of crystalline structure after annealing, which could be correlated to the accompanied changes in dielectric properties. Furthermore, significant improvements in the dielectric responses were observed in this system. After annealing, a huge increase of up to 200% occurred in the dielectric constants, especially near the temperature of maximum dielectric constant.

Dielectric properties Ca-substituted barium strontium titanate ferroelectric ceramics

The dielectric and ferroelectric properties of Ba 1− x Sr x TiO 3 (BST) ( x = 0.10 , 0.20 , 0.30 , 0.40 and 0.60) ceramics and Ba 1−2 x Sr x Ca x TiO 3 (BSCT) ( x = 0.10 , 0.20 , 0.30 ) ceramics have been investigated. The low temperature phase transitions of BST ceramics vanish after Ca 2+ substitution while the high temperature transition is diffused and relaxed, which becomes more obvious with increasing x . Ca 2+ substitution obviously decreases the dielectric constant maximum, K m , of BST ceramics and changes the temperature of dielectric constant maximum, T m , of BST ceramics. The shift of T m in BST is attributed mainly to the Sr 2+ and Ba 2+ concentration. BST ceramics exhibit almost normal ferroelectric characteristics, while a typical relaxor behavior was observed in BSCT ceramics. The relaxor behavior observations may be understood by a random electric field induced domain state.

The effect of alkali niobate addition on the phase stability and dielectric properties of Pb(Zn1∕3Nb2∕3)O3 based ceramic

While Pb(Zn1∕3Nb2∕3)O3–PbTiO3 (PZN-PT) single crystals have shown superior ferroelectric properties, less scientific and technical interests have been placed on PZN-PT polycrystalline ceramics due to their poor thermodynamic stability and the difficult processing conditions. Here, we stabilized the PZN-PT based ceramics by adding alkali niobates such as NaNbO3 (NN) and KNbO3 (KN) and investigated their structure and dielectric properties. Two stabilization mechanisms are suggested in alkali niobate added PZN-PT ceramics, increased tolerance factor and enhanced electronegativity difference. KN stabilized the perovskite structure of PZN-PT based ceramics more effectively than NN. Both PZN-PT-KN and PZN-PT-NN ceramics showed the typical behavior of relaxor ferroelectrics. The temperature of maximum dielectric constant of PZN-PT-NN was slightly higher than that of the PZN-PT-KN, which was explained by the difference in ionic size and B-site ordering.

Dielectric Properties and Relaxor Behavior of PIN Based System

Several compositions in the two PIN based systems (1-x)Pb(In0.5Nb0.5)O3-(x)PbTiO3 and (0.8-x)Pb(In0.5Nb0.5)O3-(x)PbTiO3–0.2BaTiO3 (x = 0.0, 0.1, 0.2 and 0.3) were synthesized via the wolframite method. Dielectric properties were measured in the frequency range between 100 Hz and 100 kHz and were analyzed for understanding relaxor behavior in the system. The temperature dependence of the dielectric properties was analyzed by studying the deviation from the Curie-Weiss law while the frequency dependence of the dielectric properties was analyzed by the Vogel-Fulcher relation. The results showed that the addition of BT increased the dielectric constant and decreased the shift of the maximum dielectric constant temperature (Tm) of (1-x)PIN-(x)PT compositions. Finally, the analysis also confirmed that, when added to PIN, PT decreased and BT increased the relaxor behavior of the PIN-based ceramics.

PROPERTIES OF SOL-GEL DERIVED BISMUTH-BASED PYROCHLORE THIN FILMS

ABSTRACT A new type of bismuth-based relaxor, such as Bi2(Y1/2Nb1/2)2O7 and Bi2(Mg1/3Nb2/3)2O7 thin films were fabricated on Pt/Ti/SiO2/Si substrate by a sol-gel spin coating process. The films exhibit characteristic diffused phase transition. The temperature dependent reciprocal dielectric constant characteristics of the films deviates from the Curie-Weiss law in the temperature range over the dielectric constant maximum temperature (T m ). The diffuseness of the phase transition of the thin films was estimated by calculating the difference between T m and T cw (starting temperature following the Curie-Weiss law). For the thin films annealed at 750°C, the temperature T m , the Curie-Weiss temperature Θ, the Curie-Weiss constant c and the temperature T cw were measured at frequency of 103 Hz, respectively.