Conventional Ceramic Processing Research Articles

Effect of MnO on the microstructure and electrical properties of SnO2–Zn2SnO4 ceramic composites

This work presents the microstructure and electrical properties of MnO-doped SnO2–Zn2SnO4 ceramic composites prepared through conventional ceramic processing. Scanning electron microscopy images reveal that all samples have a compact structure. With increasing MnO content, the grains grow larger and the grain boundaries become unsharp. Energy dispersive spectroscopy results for the sample doped with 0.1 mol% MnO indicate that Mn distributes randomly on the grain surfaces. X-ray diffraction patterns exhibit that all the samples are composed of SnO2 and Zn2SnO4, and the relative intensity of the diffraction peak for Zn2SnO4 increases with increasing MnO content. The relations between the electric field and current density show that all the samples have varistor properties. For the samples doped with 0.2 and 0.3 mol% MnO, the breakdown electric field is so large that it exceeds the measuring range of the instrument, whereas the relative permittivity is as low as about 30 at 100 Hz. In the electric modulus spectra, two sets of relaxation peaks were observed and the corresponding activation energies are enhanced greatly by doping MnO. The effect of MnO on the microstructure and electrical properties indicates that the space charges trapped by oxygen vacancies are the origin of the great permittivity and varistor properties for SnO2–Zn2SnO4 ceramic composites.

Heavily donor-doped, optically translucent ferroelectric barium titanate ceramics through defect chemical engineering

The possibility of preparing translucent ferroelectric heavily donor-doped BaTiO3 ceramics rich in TiO2 has been demonstrated by conventional ceramic processing based on the synthesis via the solid state route and on subsequent sintering and annealing at high levels of oxygen partial pressure.

Fabrication and electrical characterization of (Bi0.49Na0.49Ba0.02)TiO3-PVDF thin film composites

The barium doped bismuth sodium titanate (i.e., Bi0.49Na0.490.98Ba0.02)TiO3 (BNBT) powder was prepared by a conventional ceramic processing route. The thin film composites of BNBT- PVDF (polyvinylidene fluoride) were fabricated via a solution casting route. The scanning electron micrographs of the thin film samples show the homogenous distribution of grains with absence of cracks/pores. It is observed that with the increase of BNBT content in PVDF leads to enhancement in the dielectric permittivity and the reduction in the dissipation factor (tangent loss). The various electrical properties of the thin film samples were studied in the frequency range of 1 kHz to 1 MHz at different temperature between 25 and 100 °C. The prepared composite films have been used to study the (a) relationship between properties and crystal structure and (b) relaxation and conduction mechanism through the complex modulus and impedance spectroscopy. The contribution of grains was analyzed in the composite films by the fitting of equivalent circuit with the experimental data. An existence of the non-Debye type of dielectric relaxation was indicated by studying of the impedance and modulus parameters. The calculated activation energy from the temperature dependence of AC conductivity depicts hopping nature of charge carriers, which further explain the conduction process and mechanism in the prepared composites.

The evolution of phase structure, dielectric, strain, and energy storage density of complex-ions (Sr1/3Nb2/3)4+ doped 0.82Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3 ceramics

Lead-free Bi0.5(Na0.82K0.18)0.5Ti1-x(Sr1/3Nb2/3)xO3 (abbreviated as BNKT-xSN, x = 0.02–0.045) ceramics were fabricated via the conventional ceramic process, and the (Sr1/3Nb2/3)4+ complex-ions were used to modify the phase transition and multifarious electrical responses of BNKT-xSN ceramics. The SN complex-ions absolutely incorporate into the lattice of BNKT matrix to form perovskite structure. The grain morphologies and size are almost unaffected by SN complex-ions. The phase transition concerning ferroelectric type transforming into ergodic relaxor happens with increasing SN content, and the corresponding critical point is x = 0.035. The phase transformation process results in the improvement of energy storage density (W = 0.754 J/cm3) at 80 kV/cm and a high bipolar strain (S = 0.25%) with small hysteresis. The dielectric constant at Tm peaks gradually decreases with increasing SN content, and the ferroelectric-relaxor transition temperature (TF-R) is depressed to room temperature. The evolution behaviors might facilitate our cognition about the mechanism between phase structure and multiple electrical properties of BNT-based ceramics.

Dielectric and piezoelectric properties of Sm3+ doped lead barium niobate (PBN) ceramics

Rhombohedral samarium doped Lead based ceramic materials were fabricated by a high temperature conventional solid state mixed oxide ceramic process. The ceramic composition Pb1-x-3y/2BaxRey3+ Nb2O6 (x = 0.35 and y = 0.00, 0.02, 0.04 and 0.06, Re3+ = Sm3+). The pure and Sm3+ doped lead barium niobate ceramic materials are single phase with rhombohedral(hexagonal) symmetry obtained from powder x-ray diffraction (XRD). The grain size has been measured for all the compositions and lying between 1.60 and 2.90 μm. Broad dielectric peak phase transitions observed with temperature in pure and Sm3+ ion modified lead barium niobate ceramic materials. It is observed that the high values of piezoelectric charge coefficients in d31 and d33 in Sm3+ doped lead barium niobate ceramics. The mechanical quality factor Qm and d33 increases with increase of Sm3+ ion concentration and indicating a highly polarisable lead ion contributing to high Curie temperature dielectric constant.

Microstructure and enhanced dielectric properties of BaTiO 3 –SiO 2 nanocomposites using hydrogen treated nanoparticles

BaTiO 3 (BT) nanoparticles treated in H 2 and then coated with a layer of SiO 2 were used as the starting material to synthesise BT-SiO 2 nanocomposites through the conventional ceramic process. A denser morphology was obtained in the BT-SiO 2 composites. The H 2 treatment induced not only the oxygen vacancies, but also other changes (i.e. ionic disorders) in the BT. These ionic disorders were more permanent and enhanced the reaction between the BT and SiO 2 during the sintering process. Comparing with the nanocomposites sintered from the untreated BT nanoparticles, the nanocomposites sintered from the H 2 treated BT nanoparticles exhibit an enhanced dielectric performance (i.e. a higher dielectric constant and a high electric breakdown field). Among the temperatures (i.e. 850, 900, 950 and 1000°C) used to treat the BT nanoparticles in H 2 , it is experimentally found that 950°C is the best. For example, for the composites with 20 wt% SiO 2 , the dielectric constant is enhanced more than four times and the breakdown field is enhanced by about 30%. It is believed that the enhancement in the dielectric response is due to the dipoles formed by the ionic disorders, especially the acceptor defects.

Magnetic properties of Ce doped M-type strontium hexaferrites synthesized by ceramic route

This paper highlights the experimental study of Ce3+ ions doped M-type hexaferrite Sr1−xCexFe12O19 (0.00 ≤ x ≤ 0.30) prepared by adopting the conventional ceramic process. The M-type hexagonal structure is confirmed in the X-ray diffraction measurements. There were two phases recognized for the magnetic powders with varying Ce content, one in-between x = 0.00 to 0.20 as a single magneto plumbite segment and the other at x ≥ 0.20 as a second phase or the so called α-Fe2O3 phase. The micrographs of the sintered magnets depicted hexagonal crystal shapes. For magnetic properties a systematic study was done on the room temperature B–H hysteresis measurements. The estimated remanence value first increases with x in the range of x = 0.00 to 0.15 and then showed a decrease at x ≥ 0.15. Besides, the intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) show decreasing-increasing character while maximum energy product (BHmax) and ratio Hk/Hcj demonstrate increasing-decreasing character in the Ce doping range x of x ≤ 0.15 and x > 0.15 respectively.

Sintering and characterization of dielectric and thermal mechanical properties of (Bi1/2Na1/2)TiO3-BaTiO3 ceramics

(1-x)BNT-xBT ceramics were prepared by conventional ceramic processing. The determination of the optimized sintering conditions allowed to the production of high density ceramics free from secondary phase. Dielectric and thermal mechanical properties of unpoled samples were determined from cryogenic temperatures to 850 K. The results revealed that the temperature in which an anomaly is observed from the thermal strain curve coincides reasonably with the so-called depolarization temperature characterized by dielectric measurements. While the Burns temperature for traditional relaxors can be determined by dielectric and thermal mechanical measurements and agree with each other, for the (1-x)BNT-xBT ceramics these measurements did not revealed such accordance.

Electrical properties of Y/Mg modified NiO simple oxides for negative temperature coefficient thermistors

AbstractThe semiconductors based on simple oxide have unique features with controllable electrical property by element doping. Y3+ doped NiO (Ni1−xYxO, x ≤ 0.01) and Mg2+ substituted Ni0.995Y0.005O (Ni0.995−yY0.005MgyO, y ≤ 0.5) powders were synthesized by a wet chemical method. The related ceramics were obtained by conventional ceramic processing. Phase component, microstructure, electrical property and temperature sensitivity of the prepared ceramics were investigated. All ceramics have a rock‐salt type crystalline structure. The room‐temperature resistivity of the ceramics can be widely adjusted from 254 to 12 322 Ω·cm by changing the concentrations of Y3+ and Mg2+ ions. The samples show typical characteristics of negative temperature coefficient of resistivity and have high temperature sensitivity with material constants higher than 4745 K. The analysis of impedance spectra indicates that the electrical properties resulted from both grain effect and grain boundary effect. Both band conduction and small polaron hopping were proposed as possible conduction mechanisms in the studied ceramics.

Electrical property and temperature sensitivity of NiFe2−xSb x O4 (x ≤ 0.02) ceramics for negative temperature coefficient thermistors

The NiFe2−xSb x O4 (x = 0.0, 0.008, 0.01, 0.015, 0.02) ceramics were prepared by a wet chemical process. The related ceramics were obtained by powders compacting and sintering by conventional ceramic processing. The phase component, cationic valence and electrical properties of the prepared ceramics were investigated. The investigation results indicate that NiFe2−xSb x O4 ceramics have a cubic spinel structure and display a typical characteristic of negative temperature coefficient (NTC) of resistivity. The room temperature resistivity of NiFe2−xSb x O4 ceramics can be adjusted from 75597 to 2714 Ω cm by changing the contents of Sb, and the ceramics hold high thermal sensitivity with NTC material constants between 3612 and 5408 K. The investigation of impedance spectra measured at different temperatures revealed that the grain effect and grain-boundary effect contribute simultaneously to the electrical conductivity and NTC effect. Conduction mechanism of NiFe2−xSb x O4 NTC thermistors are proposed to follow the polaron hopping model.

Electrical properties and temperature sensitivity of Li/Mg modified Ni0.7Zn0.3O based ceramics

Li/Mg modified Ni0.7Zn0.3O powders with nominal compositions of [(Ni0.7Zn0.3)1-xMgx]1-yLiyO (x ≤ 0.5, y ≤ 0.06) were prepared through a wet chemical synthesis method. The powders were compacted and sintered by the conventional ceramic processing to obtain the related ceramics. The X-ray diffraction analysis indicates that all the ceramics have single phase with cubic structure and exhibit typical effect of negative temperature coefficient (NTC) of resistivity. The adjustable room-temperature resistivity (ranging from 22 Ω cm to 13.621 kΩ cm) and thermal-sensitivity constant (changing from 2444 K to 5613 K) of ceramics were achieved by altering the cationic concentrations of Li+ and Mg2+. The complex impedance analysis reveals that both grain effect and grain boundary effect contribute collectively to the electrical conduction and NTC feature of the ceramics. The possible conduction models including polaron hopping conduction and band conduction were proposed accordingly.

Improving densification and electrical properties of KNN-based lead-free piezoceramics via two-step sintering method

ABSTRACTThe 0.95(Li0.03Na0.5K0.47)(Nb0.92Sb0.05Ta0.03)O3-0.05(Ba0.5Ca0.5)ZrO3 (LNKNST-BCZ) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing via the two-step sintering method. The phase structure purity and electrical properties of the LNKNST-BCZ ceramics can be improved further by tailoring the sintering temperature and sintering time. Rather pure perovskite structure with the coexistence of ferroelectric rhombohedral (R) and tetragonal (T) phases can be obtained in the LNKNST-BCZ ceramics via the two-step sintering method confirmed by the X-ray diffraction (XRD) analysis. Sintered at optimized conditions the LNKNST-BCZ ceramics present high densification and rather homogeneous microstructure morphology. The Curie-Weiss law and the quadratic law fitting prove that the dielectric behavior of the LNKNST-BCZ ceramics approaches closer to the normal ferroelectrics with slight diffused phase transition characteristic. The LNKNST-BCZ ceramics sintered at 1180°C for 0.5 h exhibit the optimum dielectric, ferroelectric and piezoelectric properties. The improvement of the densification and piezoelectric properties of the LNKNST-BCZ ceramics can be attributed to the polymorphic R-T phase boundary and densified microstructure morphology induced by (Ba0.5Ca0.5)ZrO3 (BCZ) doping and two-step sintering method.

High dielectric tunability in composites prepared using SiO2 coated Ba0.5Sr0.5TiO3 nanoparticles

Ba0.5Sr0.5TiO3 (BST) nanoparticles were coated with SiO2 using a chemical process. SiO2-coated BST was used as the starting material to prepare BST-xSiO2 (x = 0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt%) composites via a conventional ceramic process. The influence of SiO2 on the structure and properties of these composites was systematically studied. Scanning electron microscopy (SEM) results showed that the porosity of the composites was obviously reduced by the addition of SiO2. X-ray diffraction (XRD) results indicated that, besides the perovskite phase of BST, a traceable secondary phase of BaTiSiO5 also existed. The formation of BaTiSiO5 was due to the reaction between SiO2 and barium from BST. This resulted in a lower phase transition temperature of BST phase in the composites. It was found that the dielectric constant and loss decreased with increasing SiO2 content. All the composites exhibited a low dielectric loss (< 0.01) and an almost frequency independent dielectric constant in a frequency range from 100 Hz to 100 kHz. All the composites exhibited a high tunability (> 47%). Although the tunability decreased with increasing SiO2 content, a higher tunability was achieved in the composites because the composites exhibited a much higher breakdown strength than the pure BST ceramics. Additionally, it was found that the tunability of the composites increased with the decrease of the operating temperature.

Direct fabrication of compositionally graded Ti-Al2O3 multi-material structures using Laser Engineered Net Shaping

Laser Engineered Net Shaping (LENS™), which is a laser based additive manufacturing method, was utilized to fabricate Ti-Al2O3 compositionally graded structures. The Ti-Al2O3 graded composites consisted of different sections −Ti6Al4V alloy, Ti6Al4V + Al2O3 composites, and pure Al2O3 ceramic. After LENS™ processing, microstructural characterization, phase analysis, elemental distribution, and microhardness measurements were performed on the cross sections of Ti-Al2O3 graded composites. Each section had their unique microstructures and phases. Moreover, hardness measurements demonstrated that the pure Al2O3 section had the highest hardness of 2365.5 ± 64.7 HV0.3. Conventional ceramic processing requires extensive post-processing including high temperature sintering, which makes it difficult for direct fabrication of metal-ceramic multi-layer structures. The results demonstrate that LENS™ can be utilized to process multi-material metal ceramic composites in a single step while maintaining the size, shape and compositional variations based on computer aided design files. Since this is a first-generation work, and limited research results are available in published literature related to LENS™ processing of both metals and ceramics in one operation, the demonstration of this work is expected to inspire future studies on manufacturing of multi-material composites using AM.

Hierarchical micro-nanostructured albite-based glass-ceramic for high dielectric strength insulators

A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94% Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1 MHz, low dielectric losses, (∼10−3 at 1 MHz, and a large dielectric strength, ∼60 kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.

Effects of different compositions from magnetic and nonmagnetic dopants on structural and electrical properties of ZnO nanoparticles-based varistor ceramics

In the current study, 20 nm zinc oxide (ZnO) nanoparticles were used to manufacture high-density ZnO discs doped with Mn and Sn via the conventional ceramic processing method, and their properties were characterized. Results show that the dopants were found to have significant effects on the ZnO varistors, especially on the shape and size of grains, which are significantly different for both dopants. The strong solid-state reaction in the varistor from the 20 nm ZnO powder during the sintering process may be attributed to the high surface area of the 20 nm ZnO nanoparticles. Although Mn and Sn do not affect the well-known peaks related to the wurtzite structure of ZnO ceramics, a few of the additional peaks could be formed at high doping content (≥2.0) due to the formation of other unknown phases during the sintering process. Both additives also significantly affect the electrical properties of the varistor, with a marked changed in the breakdown voltage from 415 V to 460 V for Sn and from 400 V to 950 V for Mn. Interestingly, the electrical behaviors of the varistors, such as breakdown voltage, nonlinear coefficient, and barrier height, are higher for Mn- than Sn-doping samples, and the opposite behaviors hold for hardness, leakage currents, and electrical conductivities. Results show that the magnetic moment and valence state of the two additive dopants are responsible for all demonstrated differences in the electrical characteristics between the two dopants.

Manipulation of Nanoscale Intergranular Phases for High Proton Conduction and Decomposition Tolerance in BaCeO3 Polycrystals.

In many ion-conducting polycrystalline oxides, grain boundaries are generally accepted as rate-limiting obstacles to rapid ionic diffusion, often resulting in overall sluggish transport. Consequently, based on a precise understanding of the structural and compositional features at grain boundaries, systematic control of the polycrystalline microstructure is a key factor to achieve better ionic conduction performance. In this study, we clarify that a nanometer-thick amorphous phase at most grain boundaries in proton-conducting BaCeO3 polycrystals is responsible for substantial retardation of proton migration and moreover is very reactive with water and carbon dioxide gas. By a combination of atomic-scale chemical analysis and physical imaging, we demonstrate that highly densified BaCeO3 polycrystals free of a grain-boundary amorphous phase can be easily fabricated by a conventional ceramic process and show sufficiently high proton conductivity together with significantly improved chemical stability. These findings emphasize the value of direct identification of intergranular phases and subsequent manipulation of their distribution in ion-conducting oxide polycrystals.

Facile preparation and performance of novel high-TC xBi(Ni1/2Ti1/2)O3-(1-x)Pb(Zr1/2Ti1/2)O3 piezoceramics

High Curie temperature (TC) xBi(Ni1/2Ti1/2)O3-(1-x)Pb(Zr1/2Ti1/2)O3 (xBNT-(1-x)PZT, BNT-PZT) piezoelectric ceramics were prepared by the conventional ceramic processing. The composition-induced morphotropic phase boundary (MPB) and its influences on structure and electrical performance were investigated. The synthesized BNT-PZT ceramics exhibit rather pure perovskite structure, and densified microstructure morphology with uniform elementals distribution in both grains and grain boundaries. With increasing the content of Bi(Ni1/2Ti1/2)O3 (BNT), crystal structure of the BNT-PZT ceramics transform from tetragonal phase to rhombohedral phase, and dielectric response peaks change from narrow shape to very broad shape but all presenting dielectric frequency dispersion. The diffused and relaxation dielectric behavior can be fitted well by the quadratic law, and the Vogel-Fulcher law fitting provides additional information on the relaxation characteristic. The MPB effects are confirmed further by ferroelectric and piezoelectric properties measurements. High-TC combined with excellent piezoelectric performance can be realized in the BNT-PZT system, which presents promising applications in geothermal exploration, aerospace and related elevated temperatures fields.

Rice Husk Ash as a Raw Material to Produce Willemite Pigments

This study focuses in the synthesis of ceramic pigments based on the crystal structure of willemite (Zn2SiO4). The willemite obtained from the combination of commercial zinc oxide and rice husk ash is produced in a conventional ceramic process without the use of mineralizer agent and with the addition of cobalt oxide or nickel oxide as the source of chromophore ions. The synthesis temperature used was 1200°C. The characterization of pigments involves the use of X-ray diffraction and scanning electron microscopy. The pigments applied in matte enamel and sintered at 1100°C or 1200°C developed color between blue and beige. The construction of absorbance curves showed the color development behavior of each pigment. The results showed the possibility of obtaining willemite, from rice husk ash and the color development efficiency of the material, besides showing the interference of chromophore ion (Ni and Co) in color development.

Fabrication of M-type ferrites with high La-Co concentration through Ca2+ doping

Ca2+ doped Sr0.45-xCaxLa0.55Fe11.6Co0.4O19 (x = 0, 0.15, 0.3, and 0.45) ferrites were fabricated through a conventional ceramic process. The influences of Ca2+ doping on the microstructure and magnetic properties of ferrites were investigated. Ca2+ doping could mitigate the presence of impurity phase (CoFe2O4) in ferrites. Single phase M-type ferrites could be fabricated when x ≥ 0.3. Additional Co2+ ions entered the crystal lattice and preferentially occupied the 4f2 site with Ca2+ doping. This effect greatly improved the remanence (Br) and intrinsic coercivity (Hcj) when x increased from 0 to 0.3. The average grain size of sintered ferrites slightly increased with the amount of doped Ca2+ ions. This behavior led to the deterioration of Hcj when x increased from 0.3 to 0.45. Consequently, ferrite prepared with x = 0.3 presented the highest maximum energy product ((BH)max) of 5.24MGOe. This performance is much higher than that of conventional La-Co substituted Sr-ferrites.