Effects of Glass Phase Additions and Stoichiometry on the Ba(Zn<Subscript>1/3</Subscript>X<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> (<Emphasis Type="Italic">X</Emphasis> = Ta or Nb) Sinterability and Dielectric Properties

Ba(Zn_1/3X_2/3)O₃ materials where X = Ta or Nb (respectively named BZT and BZN) exhibit attractive properties suitable for applications in type I Multi Layer Ceramics Capacitors (MLCC). Nevertheless, to produce such components using Base Metal Electrodes such as copper, a significant reduction of their sintering temperature is required. The aim of this work is first to study the effects of glass phases additions and secondly the stoichiometry influence on the sintering temperature of BZT and BZN. It is shown for example, that our materials can be sintered in air at a temperature lowered by 450C when sintering agents (B₂O₃ with LiF) are combined with a slight non-stoichiometry. The sintered samples are characterised in terms of final density, microstructure and phase content and it was underlined that such modifications (additions and stoichiometry) does not affect the dielectric properties.     

Piezoelectric and Magnetoelectric Properties of Lead Zirconate Titanate/Ni-Ferrite Particulate Composites

Piezoelectric and magnetoelectric properties of magnetoelectric particulate composites with Lead Zirconate Titanate (PZT) and Ni-ferrite were investigated. The maximum magnetoelectric voltage coefficient, (dE/dH)_max, increased with higher sintering temperature up to 1250°C. Composites sintered at 1300°C, had dissolution of Fe ions into PZT, or interdiffusion between PZT and ferrite. Connectivity of the ferrite particles and sintering temperature were important factors for fabrication of this particulate composite. The composite added with 20 wt.% amount of Ni-ferrite, sintered at 1250°C for 2 hours, had the highest magnetoelectric voltage coefficient of 115 mV/cm · Oe at room temperature. This value is comparable to that of the BaTiO₃-CoFe₂O₄ based composites reported by Philips laboratory, and is 44% higher than other magnetoelectric particulate composites.     

Synthesis and characterization of nanocrystalline Barium Strontium Titanate powder via sol-gel processing

Barium Strontium Titanate (BST) solid solution is a strong candidate material for application in tunable ferroelectric devices. In this research, we have synthesized and characterized nanocrystalline BST (Ba_0.7Sr_0.3TiO₃) powder with average particle-diameter of 15 nm through a simple sol-gel process, using barium acetate, strontium acetate and titanium isopropoxide as the precursors. In this process, stoichiometric proportions of barium acetate and strontium acetate were dissolved in acetic acid followed by refluxing, and addition of titanium (IV) isopropoxide to form BST gel. The gel was analyzed using Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). The as-formed gel was dried at 200 °C and then calcined in the temperature range of 400 to 800 °C for crystallization. Phase evolution during calcination was studied using X-ray diffraction (XRD) technique. Particle size, morphology and the lattice fringes of the calcined powder were characterized by high-resolution transmission electron microscopy (HR-TEM). To study the effects of sintering on BST nanopowder, green ceramic specimens were prepared by uniaxial compaction and then sintered at 950–1,100 °C under atmospheric conditions. Sintered specimens were analyzed for phase composition, grain size and geometric bulk density.     

Electrical properties of conventional and microwave sintered lead free magnetoelectric composites

Abstract

Here we report comparison of dielectric properties of composition synthesized by microwave and conventional sintering. Microwave sintering requires less time and temperature to achieve the same quality of materials as sintered by conventional route. The material sample was prepared by conventional solid state method and sintered in conventional & microwave furnace. Sintered samples were then subjected to XRD analysis. X-ray diffraction revealed the formation of single phase material. The dielectric and ferroelectric properties were recorded for both the samples and properties were found to improve in microwave sintered samples. There is also a significant improvement in density by microwave processing.     

Elastic Properties of Barium Zirconate Titanate Ceramics

In the paper the influence of zirconium admixture on the structure and material constants of polycrystalline ferroelectric materials BaZr_xTi_1-xO₃ (BZT) was examined. The barium zirconate titanate samples were prepared by a conventional solid state reaction method. A single phase with perovskite structure of the samples, was identified by an X-Ray diffraction technique at room temperature. The performed EDS study revealed that the samples were perfectly sintered and the material was chemically homogeneous. The dependence of shear modulus G on sample composition is similar to the respective dependence of Young's modulus E, whereas the Poisson's ratio ν decreases with the increase in zirconium concentration.     

Dielectric properties of Bi2O3–ZnO–Ta2O5 ceramics sintered by microwave

Here we report dielectric studies carried out on a Bi₂Zn_2/3Ta_4/3O₇ (abbreviated as β-BZT) composition. The material was synthesized by conventional ceramic method and microwave sintering processing. The dielectric properties were studied as a function of frequency and temperature. Dielectric constant of Bi₂Zn_2/3Ta_4/3O₇ ceramics prepared from microwave is slightly smaller than that of the conventional sintered ones. The dissipation factor and temperature coefficient of dielectric constant are low for microwave-sintered samples. Microwave sintering of Bi₂Zn_2/3Ta_4/3O₇ ceramics led to higher densification and the fine microstructure in much shorter time duration compared to conventional procedures, improved microstructure and dielectric properties. To achieve the same densification, it requires 4 h of soaking at the same temperature in conventional sintering process. Microwave sintering method may lead to energy savings because of rapid kinetics of synthesis.     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Synthesis and characterization of PZT: CF magnetoelectric composites

Here, we report the structural, dielectric, ferroelectric, piezoelectric and magnetic properties of ME composites of Lead Zirconate Titanate (PZT) and Cobalt ferrite (CF) with compositional formula (1?x) PbZr_0.55Ti_0.45O₃ + (x) CoFe₂O₄, (x = 0.00, 0.05, 0.10, 0.15 and 1.00 by weight). The samples were synthesized by conventional solid state reaction. The formation of perovskite tetragonal and spinel structure in the composites are confirmed by X-ray diffraction studies. Microstructural study of all samples was done by SEM analysis and average grain size was also calculated. The dielectric properties of samples were studied as a function of frequency and as a function of temperature (30°C – 500°C) respectively. P-E hysteresis loop at room temperature and piezoelectric coefficient were measured to study the ferroelectric and piezoelectric properties. To confirm the ferromagnetic behavior of the composites M-H hysteresis loop measurement was carried out. The Magnetoelectric voltage coefficient (dE/dH) was measured as a function of applied DC magnetic field. The maximum ME output of 389μV/ (cm.Oe) was observed for the composite with x = 0.15.     

Low-temperature sintering and microwave dielectric properties of ZnTiO3-based LTCC materials

The low-temperature sintered microwave dielectric ceramics with composition of ZnTiO₃-0.25TiO₂ were prepared by adding a small amount of low-melting compounds CuO-V₂O₅-Bi₂O₃ (CVB). The phase relationship and dielectric properties as a function of sintering temperature and the additional amount were studied. It is demonstrated that the addition of low-melting CVB can suppress the formation of Zn₂TiO₄ at low temperature, but decrease the decomposition temperature of ZnTiO₃. The sintering temperature has a significant effect on the stability of ZnTiO₃ and dielectric properties of sintered ceramics. CVB addition can promote the densification of ceramics through liquid-phase sintering. The dense 2wt% CVB-doped ZnTiO₃-0.25TiO₂ ceramics prepared at 850 °C have excellent dielectric properties of ??=?30, Q×f?=?32,000 GHz, and τ _f ?=?+12 ppm/ °C.     

Normal sintering and electric properties of (K,Na,Li)(Nb,Sb)O3 lead-free piezoelectric ceramics

0.94(K₀₅Na_0.5)NbO₃?0.03LiNbO₃?0.03LiSbO₃ (KNLNS) lead-free piezoelectric ceramics were prepared by conventional mixed oxide route with normal sintering method. The samples were sintered at different temperatures with KNLNS powder atmosphere to prevent volatilization of alkali metal oxides at high temperature. The effects of sintering temperature on the density, structure and electric properties of KNLNS ceramics were studied. X-ray diffraction (XRD) results showed that the crystal structure of the crushed KNLNS ceramic powders were pure perovskite phase with tetragonal phase structure when sintered at T????1080°C. However a K₃Li₂Nb₅O₁₅ phase with tetragonal tungsten bronze structure began to appear when the sintering temperature was higher than 1080°C. The optimum sintering temperature was 1080°C which was determined by measuring the density of the samples. Scanning electron microscope (SEM) observation indicated that the sintering temperature had a great effect on the microstructure of the samples. The KNLNS ceramics under the optimum sintering temperature showed excellent electric properties: ???=?4.29 g/cm³, ?? _r?=?826, tan???=?0.049, d ₃₃?=?190 pC/N, k _p?=?0.30, and T _c?=?385°C. The results show that the KNLNS ceramics are promising candidate for lead-free piezoelectric ceramics.     

Sintering Behaviour of BaxSr1-xTiO3

This paper deals with the sintering behaviour of Barium Strontium Titanate (BST). Two methods were examined; method 1: BaTiO₃ + SrTiO₃ source powders; method 2: BaCO₃ + SrCO₃ + TiO₂ source powders. Commercially available 50 nm BST (x = 0.60) powder was used to investigate the effect of particle size on activation energy (E_a). Discs were sintered in a Netzsch 402C Dilatometer and E_a for the powders were obtained by applying the Arrhenius expression. The results indicate powders made from both methods display a varying trend in E_a over a range of x. The commercial powder yielded a higher E_a compared with powder made from method 1.     

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

Microwave Hydrothermally Synthesized Nanocrystalline Co-Zn Ferrites

Co-Zn ferrite nano-powder was synthesized using the Microwave- Hydrothermal (M-H) method. The powder was characterized using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Fourier Transform Infrared spectroscopy (FT-IR). The densification of nanoferrites was done using two methods: a) conventional and b) microwave sintering. Electrical and magnetic properties of the sintered samples were measured at room temperature. Electrical properties such as dielectric constant (?'), dissipation factor (D), initial permeability (μ_i) and quality factor (Q) were measured over a wide frequency range (10 kHz to 1 MHz). The Curie temperature has been determined from the permeability versus temperature plots. It was found that the enhanced electrical and magnetic properties were observed for microwave sintered samples.     

Effect of seed layers on dielectric properties of Ba(Zr0.3Ti0.7)O3 thin films

The Barium zirconium titanate Ba(Zr_0.3Ti_0.7)O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates with seed layers at the BZT/Pt interface by sol–gel process. Microstructure and structure of thin films were examined. Dielectric properties of thin films with various seed layers thicknesses were investigated as a function of frequency and direct current electric field. The tunability and dielectric constant of BZT thin films increased with increasing seed layer thickness from 0 to 20 nm, while it decreased with a further increase in thickness above 20 nm, meanwhile, the leakage current showed the similar tendency at applied electric field of 250 kV/cm. The optimized seed layer thickness for BZT thin films plays an important role in maintaining the high tunability and low leakage current, which are suitable for microwave device applications.     

Enhancement of dielectric properties by optimization of sintering condition in tungsten–bronze structured Ba5SmTi3Nb7O30 ferroelectric ceramics

In this work, polycrystalline Ba₅SmTi₃Nb₇O₃₀ tungsten–bronze structured ferroelectric ceramics were synthesized by solid-state reaction technique at different sintering temperatures and durations. The X-ray diffractograms reveal the formation of the compounds in orthorhombic crystal system. The density of the compound is observed to increase with increase in sintering temperature and duration. Scanning electron microscopy (SEM) has been used for the microstructural investigation. Detailed dielectric properties of the compounds have been studied as a function of frequency and temperature. The variations of dielectric constant $\left( {\varepsilon \prime _r } \right)$ with temperature show that the compounds undergo a diffuse type ferro-paraelectric phase transition. The dielectric constant is found to increase with the increasing sintering temperature and duration. In all the samples, the variation of dielectric loss (tan δ) with temperature is observed to be almost constant initially but it increases as temperature is increased and a peak is observed only when the material is sintered at higher temperature for longer duration. The frequency dependence of dielectric constant and loss shows a decreasing trend up to nearly 10 kHz and beyond this frequency there is almost no variation. Also, the diffusivities of the samples have been calculated and it is found to increase with increasing sintering temperature and duration.     

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO₃–xBaTiO₃ [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x?=?0.275 sintered at 990 °C exhibit enhanced electrical properties of d ₃₃?=?136pC/N and k _p?=?0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x?=?0.275 is a promising lead-free high-temperature piezoelectric material.     

Enhanced dielectric properties of Bi1.5ZnNb1.5O7 thick films via cold isostatic pressing

Dense Bi_1.5ZnNb_1.5O₇ thick films were prepared on Ag/Al₂O₃ substrates using screen-printing technology at a lower temperature of 825?°C. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of thick films. After cold isostatic pressing prior to sintering, the microstructure of thick films was improved with a more compact morphology and better dielectric properties, and the permittivity and dielectric loss of thick films sintered at 900?°C were about 160 and 0.006. The obvious tunability of thick films was also observed, and the tunability value reached about 3?% for thick films sintered at 900?°C under 400?kV/cm. The enhanced properties and low-temperature sintering made this compound a potential candidate for Low Temperature Co-fired Ceramic (LTCC).     

Crystallization,microstructures and properties of low temperature co-fired CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass-ceramic

CaO-Al₂O₃-SiO₂ glass-ceramic were prepared by melt quenching technique. The crystallization behavior and properties were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The influence of sintering temperature on phase formation, microstructure, bending strength, dielectric and thermal properties were determined. The activation energy of crystallization and the Avrami parameter were also discussed. The X-ray diffraction results show that SiO₂ phase could be found in all samples and CaSiO₃ and anorthite phases could only be observed in the samples sintered at above 875°C. The densification of glass-ceramic starts at 730°C after the liquid glass is formed and stops at 803°C. Complete densification was achieved at 875°C and the highest mechanical strength was obtained at 850°C, but density significantly decreased at higher temperatures. The coefficient of thermal expansion and the dielectric constant increase with the increasing sintering temperature. The value of the Avrami parameter (n) is ~1.6 and the apparent activation energy (E) is 298 kJ/mol.     

Relaxor behavior of piezoelectric Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics sintered at low temperature

A (100-x)Pb(Yb_1/2Nb_1/2)O₃-xPbTiO₃ [PYN-PTx] solid solution system with 49.0????×????51.0 was prepared using a conventional ceramics process and sintered at low temperature. When excess PbO was added into the PYN-PTx system, all samples were sintered at temperatures as low as 800°C with good dielectric and piezoelectric properties. It is suggested that a liquid phase with excess PbO was formed during the sintering and improved the densification of PYN-PTx ceramics at low temperatures. For the PYN-PTx binary system, it was found that the temperature dependence of the relative permittivity follows a Curie?CWeiss Law above the deviation temperature (T_D) at high temperatures. Good piezoelectric properties of d ₃₃ ?=?510 pC/N, ?? _r ?=?2800 at RT, k _p?=?0.57, and k _t?=?0.42 with T_c?=?373°C were obtained for PYN-PT49.5 ceramics sintered at 800°C for 8 h.     

The effect of calcining temperature on the properties of 0-3 piezoelectric composites of PZT and a liquid crystalline thermosetting polymer

We report on the optimisation of a recently developed high performance 0-3 piezoelectric composite comprising of the piezoelectric Lead Zirconate Titanate (PZT) powder and a liquid crystalline thermosetting matrix polymer (LCT). The matrix polymer is a liquid crystalline polymer comprising of an HBA-HNA backbone with phenylethynyl end-groups. The use of a high performance polymer makes the composite a possible candidate to be used in sensor applications at elevated temperatures. The composite properties were optimised by calcining the PZT powder at different temperatures, prior to mixing the powders into the LCT matrix. The aim is to study the effect of the calcining temperature on the piezoelectric properties of the composite The PZT powders were characterised by X-ray diffraction and scanning electron microscopy. The dielectric constant and piezoelectric charge constant (d ₃₃ ) of the composite samples was measured. It was found that a relationship exists between the calcining temperature of the PZT powder and the piezoelectric properties of the composites. A maximum voltage constant of g ₃₃  = 63 mVm/N was obtained for a composite containing 40% (by volume) of PZT powder calcined at 1150°C.