Showing papers on "Sintering published in 2016"
TL;DR: The p-i-n structure of perovskite solar cells has shown efficiencies as high as 18%, lower temperature processing, flexibility, and, furthermore, negligible J-V hysteresis effects.
Abstract: ConspectusInorganic–organic hybrid perovskite solar cells research could be traced back to 2009, and initially showed 3.8% efficiency. After 6 years of efforts, the efficiency has been pushed to 20.1%. The pace of development was much faster than that of any type of solar cell technology. In addition to high efficiency, the device fabrication is a low-cost solution process. Due to these advantages, a large number of scientists have been immersed into this promising area. In the past 6 years, much of the research on perovskite solar cells has been focused on planar and mesoporous device structures employing an n-type TiO2 layer as the bottom electron transport layer. These architectures have achieved champion device efficiencies. However, they still possess unwanted features. Mesoporous structures require a high temperature (>450 °C) sintering process for the TiO2 scaffold, which will increase the cost and also not be compatible with flexible substrates. While the planar structures based on TiO2 (regular s...
558 citations
TL;DR: This paper describes a sintering technique for ceramics and ceramic-based composites, using water as a transient solvent to effect densification by a mediated dissolution-precipitation process, named the Cold Sintering Process (CSP).
Abstract: This paper describes a sintering technique for ceramics and ceramic-based composites, using water as a transient solvent to effect densification (i.e. sintering) at temperatures between room temperature and 200 °C. To emphasize the incredible reduction in sintering temperature relative to conventional thermal sintering this new approach is named the "Cold Sintering Process" (CSP). Basically CSP uses a transient aqueous environment to effect densification by a mediated dissolution-precipitation process. CSP of NaCl, alkali molybdates and V2 O5 with small concentrations of water are described in detail, but the process is extended and demonstrated for a diverse range of chemistries (oxides, carbonates, bromides, fluorides, chlorides and phosphates), multiple crystal structures, and multimaterial applications. Furthermore, the properties of selected CSP samples are demonstrated to be essentially equivalent as samples made by conventional thermal sintering.
333 citations
TL;DR: The encapsulation of platinum species in highly siliceous chabazite (CHA) crystallized in the presence of N,N,N-trimethyl-1-adamantammonium and a thiol-stabilized Pt complex shows enhanced stability toward metal sintering in a variety of industrial conditions, including H2, O2, and H2O.
Abstract: We report the encapsulation of platinum species in highly siliceous chabazite (CHA) crystallized in the presence of N,N,N-trimethyl-1-adamantammonium and a thiol-stabilized Pt complex. When compared to Pt/SiO2 or Pt-containing Al-rich zeolites, the materials in this work show enhanced stability toward metal sintering in a variety of industrial conditions, including H2, O2, and H2O. Remarkably, temperatures in the range 650–750 °C can be reached without significant sintering of the noble metal. Detailed structural determinations by X-ray absorption spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy demonstrate subtle control of the supported metal structures from ∼1 nm nanoparticles to site-isolated single Pt atoms via reversible interconversion of one species into another in reducing and oxidizing atmospheres. The combined used of microscopy and spectroscopy is critical to understand these surface-mediated transformations. When tested in hydrogena...
292 citations
TL;DR: In this paper, the authors proposed a lead-free relaxor ferroelectric ceramics based on (K0.5Na 0.5)NbO3 without using hot isostatic pressing and spark plasma sintering.
Abstract: We prepared highly transparent relaxor ferroelectric ceramics based on (K0.5Na0.5)NbO3 using a pressure-less solid-state sintering method without using hot isostatic pressing and spark plasma sintering. A high energy storage density of 2.48 J cm−3 and high transparency in the visible region (ca. 60% at 0.7 μm) were achieved for the 0.8(K0.5Na0.5)NbO3–0.2Sr(Sc0.5Nb0.5)O3 ceramics with submicron-sized grains (about 0.5 μm). The energy storage density of 2.48 J cm−3 exceeded all previous reports for lead-free bulk ceramics. These results demonstrate that the 0.8(K0.5Na0.5)NbO3–0.2Sr(Sc0.5Nb0.5)O3 ceramics are promising lead-free transparent dielectric materials for use in transparent electronic devices. This study not only opens up a new avenue for the design of lead-free transparent ferroelectric ceramics with a high energy storage density, but also expands the applications of (K0.5Na0.5)NbO3-based ceramics into new areas beyond piezoelectric applications.
258 citations
TL;DR: In this article, the data for all reported low-loss microwave dielectric ceramic materials with ultra-low sintering temperatures are collected and tabulated, and the table of these materials gives the relative permittivity, quality factor (tan ǫ ), temperature variation of the resonant frequency, crystal structure, sinting temperature, measurement frequency and references.
Abstract: The recent rapid advances in wireless telecommunication, Internet of Things, the Tactile Internet (5th generation wireless systems), the Industrial Internet, electronic warfare, satellite broadcasting, and intelligent transport systems demand low loss dielectric materials with ultra-low sintering temperatures with modern component fabrication techniques. Properties of microwave ceramics depend on several parameters including their composition, the purity of starting materials, processing conditions, and their ultimate densification/porosity. The preparation, characterization and properties of important materials families such as glass ceramics and molybdates, tellurates, tungstates and vanadates, in combination with Bi, K, Na, Ag, Li, Ba, Ca, etc. with ultra-low sintering temperatures are discussed. In this review the data for all reported low-loss microwave dielectric ceramic materials with ultra-low sintering temperatures are collected and tabulated. The table of these materials gives the relative permittivity, quality factor (tan δ ), temperature variation of the resonant frequency, crystal structure, sintering temperature, measurement frequency and references. The data arranged in the order of increasing relative permittivity will be very useful for scientists, industrialists, engineers and students working on current and emerging applications of microelectronics.
216 citations
TL;DR: The cold sintering process (CSP) as discussed by the authors uses a transient low temperature solvent, such as water or water with dissolved solutes in stoichiometric ratios consistent with the ceramic composition, to control the dissolution and precipitation of ceramics and effect densification between room temperature and ≈200 °C.
Abstract: Co-sintering ceramic and thermoplastic polymer composites in a single step with very high volume fractions of ceramics seems unlikely, given the vast differences in the typical sintering temperatures of ceramics versus polymers. These processing limitations are overcome with the introduction of a new sintering approach, namely “cold sintering process” (CSP). CSP utilizes a transient low temperature solvent, such as water or water with dissolved solutes in stoichiometric ratios consistent with the ceramic composition, to control the dissolution and precipitation of ceramics and effect densification between room temperature and ≈200 °C. Under these conditions, thermoplastic polymers and ceramic materials can be jointly formed into dense composites. Three diphasic composite examples are demonstrated to show the overall diversity of composite material design between organic and inorganic oxides, including the microwave dielectric Li2MoO4–(C2F4 ) n , electrolyte Li1.5Al0.5Ge1.5(PO4)3–(CH2CF2 ) x [CF2CF(CF3)] y , and semiconductor V2O5–poly(3,4-ethylenedioxythiophene) polystyrene sulfonate composites. Cold sintering is more general and shall have a major impact on the processing of composite materials for many different applications, mechanical, thermal, and electronic, to mention a few possibilities. CSP concepts open up new composite material design and device integration schemes, impacting a wide variety of applications.
192 citations
TL;DR: In this paper, a new processing technique consisting of the gelcasting, sintering and vacuum infiltration methods was proposed to fabricate high performance ceramic/polymer composites for electronic packaging.
183 citations
TL;DR: In this paper, aluminum oxide powder was used for part fabrication and various build parameters (e.g., layer thickness, saturation, particle size) were modified and different sintering profiles were investigated to achieve nearly full-density parts.
173 citations
TL;DR: In this paper, a series of low temperature firing (1 − x)BiVO4-xTiO2 (x = 0.4, 0.50,0.55 and 0.60) microwave dielectric ceramics was prepared using traditional solid state reaction method.
Abstract: In the present work, a series of low temperature firing (1 − x)BiVO4–xTiO2 (x = 0.4, 0.50, 0.55 and 0.60) microwave dielectric ceramics was prepared using traditional solid state reaction method. From back-scattered electron images (BEI), X-ray diffraction (XRD) and energy dispersive analysis (EDS), there was negligible reaction between BiVO4 and TiO2 at the optimal sintering temperature ∼900 °C. As x increased from 0.4 to 0.60, permittivity (er) increased from 81.8 to 87.7, quality factor value (Qf) decreased from 12 290 to 8240 GHz and temperature coefficient (TCF) shifted from −121 to +46 ppm per °C. Temperature stable microwave dielectric ceramic was obtained in 0.45BiVO4–0.55TiO2 composition sintered at 900 °C with a er ∼ 86, a Qf ∼ 9500 GHz and a TCF ∼ −8 ppm per °C. Far-infrared reflectivity fitting indicated that stretching of Bi–O and Ti–O bonds in this system dominated dielectric polarization. This series of ceramics are promising not only for low temperature co-fired ceramic (LTCC) technology but also as substrates for physically and electrically small dielectrically loaded micro-strip patch antennas.
162 citations
TL;DR: Li2Mg3BO6 (B = Ti, Sn, Zr) ceramics with a rock salt structure were obtained in their respective sintering temperature range and their microwave dielectric properties were investigated.
Abstract: Using a conventional solid-state reaction Li2Mg3BO6 (B = Ti, Sn, Zr) ceramics were prepared and their microwave dielectric properties were investigated. The analysis revealed that cubic Li2Mg3BO6 (B = Ti, Sn, Zr) ceramics with a rock salt structure could be obtained in their respective sintering temperature range. Three promising ceramics Li2Mg3TiO6, Li2Mg3SnO6 and Li2Mg3ZrO6 sintered at 1280 °C, 1360 °C and 1380 °C possessed out-bound microwave dielectric properties: ϵr = 15.2, 8.8 and 12.6, Q × f = 152,000 GHz (at 8.3 GHz), 123,000 GHz (at 10.7 GHz) and 86,000 GHz (at 9.3 GHz), and τf = −39 ppm/°C, −32 ppm/°C and −36 ppm/°C, respectively.
160 citations
TL;DR: In this paper, the formation and sintering behavior of TaC-HfC ceramics made from commercial TaC and HfC powders prepared using Spark Plasminar Sintering (SPS) at temperatures up to 2450°C was investigated.
Abstract: Solid solution formation and sintering behaviour of TaC–HfC ceramics made from commercial TaC and HfC powders prepared using spark plasma sintering (SPS) at temperatures up to 2450 °C was investigated. Phase analysis and lattice parameter measurements using X-ray Diffraction (XRD) showed mutual diffusion of Hf and Ta with increasing sintering temperature. High Resolution Transmission Electron Microscopy (HRTEM) confirmed that solid solution formation and densification were achieved by a solid-state mechanism. Solid solutions were achieved for 4TaC–1HfC, 1TaC–1HfC and 1TaC–4HfC powders after sintering at temperatures of at least 2350 °C. Fracture toughness ( K IC ) values were in the range of 2.7–3.4 MPa m 1/2 for all ceramics measured using Vickers indentation. Thermal conductivity of TaC was 55.8 W/m K at 1400 °C. Coefficients of thermal expansion (CTE) varied from 7.08–7.66 × 10 −6 /K (in the range of 25–2000 °C), with TaC at the lower end.
TL;DR: In this paper, the equiatomic multiprincipal CoCrFeCuNi and CoCr FeMnNi high-entropy alloys (HEAs) were consolidated via high pressure sintering from the powders prepared by the mechanical alloying method (MA).
TL;DR: The presented technique could be extended to a much broader range of material systems than previously demonstrated via a hydrothermal synthesis using water or volatile solutions, and provides a chemical roadmap for cost-effective inorganic processing that can enable broad practical applications.
Abstract: Sintering is a thermal treatment process that is generally applied to achieve dense bulk solids from particulate materials below the melting temperature. Conventional sintering of polycrystalline ceramics is prevalently performed at quite high temperatures, normally up to 1000 to 1200 °C for most ceramic materials, typically 50% to 75% of the melting temperatures. Here we present a new sintering route to achieve dense ceramics at extraordinarily low temperatures. This method is basically modified from the cold sintering process (CSP) we developed very recently by specifically incorporating the hydrothermal precursor solutions into the particles. BaTiO3 nano polycrystalline ceramics are exemplified for demonstration due to their technological importance and normally high processing temperature under conventional sintering routes. The presented technique could also be extended to a much broader range of material systems than previously demonstrated via a hydrothermal synthesis using water or volatile soluti...
TL;DR: In this article, Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO2 adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst.
Abstract: Novel Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO2 Adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst The superior reactivity of monodentate formate towards hydrogenation than that of bidentate formate species was identified by DRIFTS analysis and the formation of more active monodentate formate species was indisputably facilitated by W additives, leading to the greatly enhanced catalytic activity H-2-TPR and CO2-TPD characterization showed that doping W increased the number of stable CO2 adsorption sites and helped in anchoring the Ni sites as a result of strengthened Ni-Mg interaction, both of which were responsible for the enhanced CO2 methanation activity and the improved resistance against sintering (C) 2016 Elsevier BV All rights reserved
TL;DR: Two-step sintering (TSS) is a promising method used to obtain high-density bodies and smaller grain sizes as mentioned in this paper, and the effect of this technique on the grain density and sizes of different ceramic materials.
TL;DR: The microstructure analysis demonstrated that the formation of Cu-Cu joints was realized by metallurgical bonding at the contact interface between the Cu pad and the sintered Cu nanoparticle layer, and the densely sintering layer was composed of polycrystals with a size of hundreds of nanometers.
Abstract: Highly conductive Cu–Cu interconnections of SiC die with Ti/Ni/Cu metallization and direct bonded copper substrate for high-power semiconductor devices are achieved by the low-temperature sintering of Cu nanoparticles with a formic acid treatment. The Cu–Cu joints formed via a long-range sintering process exhibited good electrical conductivity and high strength. When sintered at 260 °C, the Cu nanoparticle layer exhibited a low resistivity of 5.65 μΩ·cm and the joints displayed a high shear strength of 43.4 MPa. When sintered at 320 °C, the resistivity decreased to 3.16 μΩ·cm and the shear strength increased to 51.7 MPa. The microstructure analysis demonstrated that the formation of Cu–Cu joints was realized by metallurgical bonding at the contact interface between the Cu pad and the sintered Cu nanoparticle layer, and the densely sintered layer was composed of polycrystals with a size of hundreds of nanometers. In addition, high-density twins were found in the interior of the sintered layer, which contri...
TL;DR: In this article, metalloorganic derived flame made nanoparticles can overcome these processing challenges resulting in a significantly reduced energy input required for densification, 10-40 fold shorter dwell times at sintering temperatures, compared to common solid state reaction derived c-LLZO.
Abstract: Ceramic electrolytes are proposed as key components in resolving challenges extant in developing next generation, high energy density Li batteries by replacing liquid electrolytes to improve safety and performance. Among numerous candidates, c-LLZO offers multiple desirable properties: high ionic conductivities (0.1–1 mS cm−1), Li stability, a wide electrochemical operating window (∼6 V) and pH stability (7–11.5). However, incorporation into prototype cells has yet to be demonstrated as c-LLZO membranes at thicknesses <50 μm have not been achieved. Processing dense, thin films matching bulk counterpart properties remains a very difficult target arising from energy and/or equipment intensive sintering, Li volatilization, and contamination from substrates. We show that using metalloorganic derived flame made nanoparticles can overcome these processing challenges resulting in a significantly reduced energy input required for densification, 10–40 fold shorter dwell times at sintering temperatures, compared to common solid state reaction derived c-LLZO. Furthermore, surface/volume ratios of the films are determined to be a critical factor affecting final microstructures and phase compositions of the sintered films. Through careful control of the processing variables, 10–15 grains thick, dense (94 ± 1%) c-LLZO thin (<30 μm), flexible films with high ambient ionic conductivities (0.2 ± 0.03 mS cm−1) are achieved using conventional casting–sintering of flame made nanoparticles. These c-LLZO membranes greatly increase the selection of complementary cell components and simplify battery configurations broadening opportunities for cell designs.
TL;DR: A protocol to achieve dense ceramic solids at extremely low temperatures via integrating the particle nanotechnology into the recently developed cold sintering process (CSP) via effectively utilizing the large surface-to-volume ratio of nanoparticles is established.
Abstract: The sintering process is an essential step in taking particulate materials into dense ceramic materials. Although a number of sintering techniques have emerged over the past few years, the sintering process is still performed at high temperatures. Here we establish a protocol to achieve dense ceramic solids at extremely low temperatures (<200 °C) via integrating the particle nanotechnology into the recently developed cold sintering process (CSP). The sintering path has been appropriately tailored via effectively utilizing the large surface-to-volume ratio of nanoparticles. BaTiO3 ceramics have been used for the illustration, given its importance in extensive electronic device applications, as well as its scientific interest, being a model material for many of the ferroelectric materials. Together with detailed experimental studies, the trends are also analyzed with a fundamental thermodynamic consideration. Such an impactful technique could have widespread application prospects in a wide variety of materi...
10 Oct 2016
TL;DR: A review of the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sinterings is presented in this article.
Abstract: During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.
TL;DR: In this paper, the effect of sintering temperature on density, microstructure, phase formation and mechanical properties of power bed binder jet printed alloy 625 parts was investigated, and the as-received powder was subjected to differential scanning calorimetry analysis, and printed samples were cured and sintered at various temperatures under high vacuum.
TL;DR: In this article, copper matrix composites reinforced with different amounts of titanium carbide particles were produced by mechanical milling and in-situ formation of reinforcements, and the changes in lattice parameter, crystallite size, lattice strain, dislocation density and Gibbs free energy changes in different samples (with different TiC particles contents) were studied by X-Ray Diffraction technique with Cu-kα radiation and using Nelson-Riley method and Williamson-Hall equation.
TL;DR: In this article, it was shown that the transition to a highly nonlinear rise in electrical conductivity, a signature event for the onset of the flash, occurs within a narrow range of power density.
Abstract: The large bank of data for ceramics from experiments in flash sintering reveal a surprising characteristic: that the transition to a highly nonlinear rise in electrical conductivity—a signature event for the onset of the flash—occurs within a narrow range of power density. This condition holds for ceramics that are semiconductors, ionic conductors, electronic conductors, and insulators.They flash at temperatures that range from 300°C to 1300°C, and at electric fields from 10 V/cm to over 1000 V/cm. Yet, the power expenditure at the transition for all of them still falls within this narrow range. This, rather uniform value of power dissipation suggests that Joule heating is a key factor in instigating the flash. A general formulation is developed to test if indeed Joule heating alone can lead to the progression of such nonlinear behavior. It is concluded that Joule heating is a necessary but not a sufficient condition for flash sintering.
TL;DR: In this paper, α-alumina samples produced by uniaxial pressing were flash sintered under electrical fields ranging from 500 to 1500 V/cm in experiments at constant heating rate and the onset temperature for flash sintering can be successfully modelled as a function of the applied voltage.
Abstract: Nearly pure α-alumina samples produced by uniaxial pressing were flash sintered under electrical fields ranging from 500 V/cm to 1500 V/cm in experiments at constant heating rate. Sintering temperature significantly decreased with the applied E-field even down to ≈900 °C at 1500 V/cm. The onset temperature for flash sintering can be successfully modelled as a function of the applied voltage. The sintering temperature is also shown to be strongly affected by the electrode materials used during the treatment: using silver or carbon electrodes the sintering temperature is about 300 °C lower than when using platinum electrodes. In addition, the bulk density and porosity of the sintered alumina ceramic correlate strongly with the imposed current limit. Power dissipation was analysed before and during flash sintering; the activation energy for conduction was calculated in both cases, indicating that the process is based on ionic diffusion phenomena. Finally, we showed that during flash sintering the activation energy for conduction decreases, suggesting the occurrence of physical or structural modifications induced by current localization at the grain boundaries.
TL;DR: In this article, a n-type SnSe compound has been synthesized through melting with spark plasma sintering, and the carrier concentration of SnSe is significantly increased, leading to a large enhancement of electrical conductivity.
Abstract: N-type SnSe compound has been synthesized through melting with spark plasma sintering. By doping BiCl3, the carrier concentration of SnSe is significantly increased, leading to a large enhancement of electrical conductivity. Meanwhile, the SnSe0.95-BiCl3 samples also exhibit higher Seebeck coefficient and lower lattice thermal conductivity, compared with polycrystalline SnSe. Consequently, a high power factor of similar to 5 mu W cm(-1) K-2 and a ZT of 0.7 have been achieved at 793 K. The synergistic roles of BiCl3 doping in SnSe provide many opportunities in the optimization of n-type SnSe materials. (C) 2016 AIP Publishing LLC.
TL;DR: In this paper, the Gibbs free energy (GFE) was used to predict the reactivity between the sintering additive and SiC, particularly for liquid phase SiC at 1700-1900°C. This was verified by the experimental results for various types of Sintering additives such as main group metals, metal oxides, and rare earth elements.
TL;DR: In this paper, a 40-layered Ti-Al composites were fabricated in a single-shot explosive welding process and the structure of the composites was thoroughly investigated using scanning and transmission electron microscopy.
TL;DR: In this paper, nanocrystalline CrMnFeCoNi HEAs were prepared by powder metallurgy and shown to have a tensile strength as high as 1000 MPa at room temperature and reasonable ductility.
TL;DR: In this article, a low-cost alumina-mullite composite hollow fiber ceramic membrane (HFCM) was fabricated via phase-inversion method followed by high temperature sintering.
Abstract: With abundant bauxite mineral as starting material, a low-cost alumina-mullite composite hollow fiber ceramic membrane (HFCM) was fabricated via phase-inversion method followed by high temperature sintering. Process parameters, including bore fluid flow rate and air-gap distance, which affect structure and properties of the HFCM were systematically explored. A low bore fluid flow rate would lead to the deformation of inner walls of the HFCM as a result of insufficient solidification, while a large air-gap distance would induce the distortion of finger-like voids. Effects of sintering on the microstructure, pore size distribution, nitrogen gas flux and mechanical properties were investigated in details. Acid-base titration was first proposed to quantitatively determine concentration of surface active sites of membrane surface after sintering. An increase in sintering temperature leads to significantly enhancing strength but almost linearly reduces concentration of active surface hydroxyl sites. Compared with its alumina counterpart, this low-cost composite membrane can be sintered at lower sintering temperature, and exhibits higher mechanical strength and active surface hydroxyl site concentration.
TL;DR: In this paper, a gas atomised AZ91 powder has been consolidated by Spark Plasma Sintering (SPS) at different temperatures in the range of 310-C-500-C. The influence of the sintering temperature on the Al 12 Mg 17 precipitation and the grain size was investigated through XRD, SEM and EDX analyses.
TL;DR: In this paper, microstructural statistics for 3 mol% yttria-stabilized zirconia synthesized by both conventional sintering and flash-sintering with AC and DC current were obtained.
Abstract: Systematic microstructural statistics for 3 mol% yttria-stabilized zirconia synthesized by both conventional sintering and flash sintering with AC and DC current were obtained. Within the gage section, flash sintered microstructures were indistinguishable from those synthesized by conventional sintering procedures. With both techniques, full densification was obtained. However, from both AC and DC flash sintered specimens, heterogeneous grain size distributions and residual porosity were observed in the proximity of the electrodes. After DC sintering, an almost 400 times increased average grain size was observed near cathode compared to the gage section, unlike areas close to the anode. Concepts of Joule heating alone were not sufficient to explain the experimental observations. Instead, the activation energy for grain growth close to the cathode is lowered considerably during flash sintering, hence suggesting that electrode effects can cause significant heterogeneities in microstructure evolution during flash sintering. Microstructural characterization further indicated that microfracturing during green-pressing and variations in contact resistance between the electrodes and the ceramic may also contribute to grain size gradients and hence local variations of physical properties.