Effect of A‐ or B‐site doping of perovskite calcium manganite on structure,resistivity, and thermoelectric properties

Bismuth‐, lanthanum‐, and molybdenum‐doped calcium manganite (CaMnO₃, abbreviated Mn113) are synthesized by solid‐state synthesis route from their respective oxide precursors at a same doping level (x=0.05). Depending on the ionic sizes, trivalent dopants (Bi³⁺ and La³⁺) replace Ca²⁺(A site), while penta/hexavalent dopant Mo⁵⁺/Mo⁶⁺ replaces Mn⁴⁺ (B site) in the Mn113 structure. XRD of all three doped samples confirm formation of single phase. In all three samples, doping causes unit cell volume to expand, while volume expansion is maximum for the Mo‐Mn113. The transport behavior of the doped samples follows small polaron hopping mechanism. Resistivity of the doped samples depends not only on the carrier concentration but also on the effective bandwidth determined by the structural distortion introduced by the dopant ions. Bi‐Mn113 has highest resistivity at the both temperature end, while La‐Mn113 has the lowest. Thermopower is determined by the carrier concentration only and does not depend on dopant type, having value ~260 μV/K at 1000 K. At high (>800 K), S reaches a saturation value and becomes independent of T. La‐Mn113 is having highest figure of merit (zT) 0.19 at 1000 K.     

Investigation of Annealing Induced Yttria Segregation in Sputtered Yttria‐Stabilized Zirconia Thin Films

8 mol% yttria‐stabilized zirconia (8YSZ) is an extensively studied solid electrolyte. But there is no consistency in the reported ionic conductivity values of 8YSZ thin films. Interfacial segregation in YSZ thin films can affect its ionic conductivity by locally altering the surface chemistry. This article presents the effects of annealing temperature and film thickness on free surface yttria segregation behavior in 8YSZ thin film by Angle Resolved XPS and its influence on the ionic conductivity of sputtered 8YSZ thin films. Surface yttria concentration of about 32, 20, and 9 mol% have been found in 40 nm 8YSZ films annealed at 1273, 1173, and 1073 K, respectively. Yttria segregation is found to increase with increase in annealing temperature and film thickness. Ionic conductivities of 0.23, 0.16, and 0.08 Scm^?1 are observed at 923 K for 40 nm 8YSZ films annealed at 1073, 1173, and 1273 K, respectively. The decrease in conductivity with increase in annealing temperature is attributed to the increased yttria segregation with annealing. Neither segregation nor film thickness is found to affect the activation energy of oxygen ion conduction. Target purity is found to play a key role in determining free surface yttria segregation in 8YSZ thin films.     

Synthesis of Ni2+‐doped ZnAl2O4/ZnO Composite Phosphor Film with Largely Enhanced Polychromatic Emission via a Single‐Source Precursor

Ni²⁺‐doped ZnAl₂O₄/ZnO composite films were successfully fabricated on single crystal silicon substrates through a single‐source precursor route, which mainly involved slurry coating of Ni–Zn–Al‐layered double hydroxide precursor followed by calcination at elevated temperatures. Material characterization has been presented using a combination of X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectra, Raman spectra, UV–vis diffuse reflectance spectra, and fluorescence spectroscopy measurements. The results showed that Ni²⁺ ions could be uniformly doped in the two‐phase ZnO and ZnAl₂O₄ lattices. A broadened and intense polychromatic emission peak covering the whole visible region was obtained over 4.3 mol% Ni²⁺‐doped ZnAl₂O₄/ZnO composite film, which was attributed to the presence of an appropriate number of luminescent Ni²⁺centers in the ZnO and ZnAl₂O₄ double host matrix, thus largely enhancing the related transition. We believe that such unique ZnAl₂O₄/ZnO films can open up a new opportunity for advanced applications of composite phosphors.     

Optimization of anode structure for intermediate temperature solid oxide fuel cell via phase‐inversion cotape casting

A functional layer and a porous support that together constitute an anode for a solid oxide fuel cell were simultaneously formed by the phase‐inversion tape casting method. Two slurries, one composed of NiO and yttria‐stabilized zirconia (YSZ) powders and the other of NiO, YSZ, and graphite were cocasted and solidified by immersion in a water bath via the phase‐inversion mechanism. The as‐formed green tape consisted of a sponge‐like thin layer and a fingerlike thick porous layer, derived from the first slurry and the second slurry, respectively. The former acted as the anode functional layer (AFL), while the latter was used as the anode substrate. The AFL thickness was varied between 20 and 60 μm by adjusting the blade gap for the tape casting. Single cells based on such NiO‐YSZ anodes were prepared with thin YSZ electrolytes and YSZ‐(La_0.8Sr_0.2)_0.95MnO_3?δ (LSM) cathodes, and their electrochemical performance was measured using air as oxidant and hydrogen as fuel. The maximum power densities obtained at 750°C were 720, 821, and 988 mW cm^?2 with the AFL thickness at 60, 40, and 20 μm, respectively. The satisfactory electrochemical performance was attributed to the dual‐layer structure of the anode, where the sponge‐like AFL layer provided plenty of triple‐phase boundaries for hydrogen oxidation, and the fingerlike thick porous substrate allowed for facile fuel transport. The phase‐inversion tape casting developed in this study is applicable to the preparation of other planar ceramic electrodes with dual‐layer asymmetric structure.     

Optical Temperature Sensing Behavior of High‐Efficiency Upconversion: Er3+–Yb3+ Co‐Doped NaY(MoO4)2 Phosphor

A class of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ upconversion (UC) phosphors have been successfully synthesized by a facile hydrothermal route with further calcination. The structural properties and the phase composition of the samples were characterized by X‐ray diffraction (XRD). The UC luminescence properties of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ were investigated in detail. Concentration‐dependent studies revealed that the optimal composition was realized for a 2% Er³⁺ and 10% Yb³⁺‐doping concentration. Two‐photon excitation UC mechanism further illustrated that the green enhancement arised from a novel energy‐transfer (ET) pathway which entailed a strong ground‐state absorption of Yb³⁺ ions and the excited state absorption of Yb³⁺–MoO₄^2? dimers, followed by an effective energy transfer to the high‐energy state of Er³⁺ ions. We have also studied the thermal properties of UC emissions between 303 and 523 K for the optical thermometry behavior under a 980 nm laser diode excitation for the first time. The higher sensitivity for temperature measurement could be obtained compared to the previous reported rare‐earth ions fluorescence based optical temperature sensors. These results indicated that the present sample was a promising candidate for optical temperature sensors with high sensitivity.     

Structural and Electrical Properties of Ni‐Substituted Mg‐Mn Nanoferrite by Coprecipitation Route

Ni²⁺ ions doped on Mg_0.40Mn_0.60‐xNi_xFe₂O₄ compositions with 0.00 ≤ x ≤ 0.60 have been synthesized by coprecipitation method and taken for the present work to study the dielectric properties and impedance characterization using the XRD and electrical measurements. The X‐ray diffraction and FT‐IR revealed that the ferrite has single‐phase cubic spinel structure. The calculated particle size from XRD data verified using SEM as well as AFM. These photographs show that the ferrites have crystalline size in the range of 20–50 nm. It was observed that the particle size decreased and Ni concentration increased. The dielectric constant and dielectric loss decreased with increase in nonmagnetic Ni²⁺ ions. Electrical properties indicate that synthesized nanoferrite particles have high resistivity.     

Synthesis of Single‐Phase Gd‐Doped Ceria Nanopowders by Radio Frequency Thermal Plasma Treatment

Gd‐doped ceria nanopowders were synthesized using Radio Frequency (RF) thermal plasma. The powders were prepared by ball‐milling Gd₂O₃ and CeO₂ powders of several tens of μm in size at the cation ratio of 8:2 and 9:1. The prepared precursors were treated by RF thermal plasma at a plate power level of ~140 kVA, and then, small‐sized powders (~50 nm) were retrieved by filtration. Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, and Selected‐Area Electron‐Diffraction images of the as‐synthesized powders showed that Gd atoms were incorporated into the CeO₂ particles. In addition, no crystalline peak for Gd₂O₃ appeared in the X‐ray diffraction patterns of the as‐synthesized powders, which is attributed to the solid solution of Gd³⁺ into the CeO₂ lattices. Finally, Inductively Coupled Plasma‐Optical Emission Spectrometry analysis data revealed relatively small changes within 3 at.% in the cation composition between the ball milled powder mixtures and the nanoscale powders prepared from these mixtures.     

Freestanding Micro‐SOFCs with Electrodes Prepared by Electrostatic Spray Deposition

We report a freestanding micro solid oxide fuel cell with both the anode and cathode deposited using electrostatic spray deposition (ESD) technique. The cell is consisted of dense yittria‐stabilized zirconia (YSZ) electrolyte (100 nm thick), porous lanthanum strontium manganite (LSM)–YSZ cathode (∼3 μm thick), and porous NiO‐YSZ anode (∼3 μm thick). LSM‐YSZ and NiO‐YSZ composite powders were initially prepared by glycine nitrate process and super‐critical fluid processes, respectively, and both cathode and anode layers were deposited by the ESD. The resulting freestanding micro cell exhibited an open circuit voltage close to the theoretical value of 1.09 V, and a maximum power density of 41.3 mWcm^–2 at 640 °C.     

Temperature Dependence of Electrical Resistivity (4–300 K) in Aluminum‐ and Boron‐Doped SiC Ceramics

Al‐ and B‐doped 3C–SiC ceramics were prepared by hot‐pressing powder compacts containing submicrometer‐sized β‐SiC, precursors of 5 wt% nanosized β‐SiC, and an optional additive (Al or B) in an Ar atmosphere. Electron probe microanalysis (EPMA) investigation on the obtained specimens revealed that a portion of the doped Al and B atoms substituted the zinc blende lattice sites. The temperature‐dependent electrical resistivity data of the Al‐ and B‐doped SiC specimens were measured in the 4–300 K range and compared with those of an undoped specimen. The Al‐ and B‐doped SiC specimens exhibited resistivities that were as high as ~10³ Ω cm at room temperature and ~10⁵ and ~10⁴ Ω cm, respectively, below 100 K. These values are larger than those of the undoped SiC specimen by a factor of ~10⁴. Such high resistivities of the impurity‐doped specimens are attributable to the carrier compensation by the Al‐ and B‐derived acceptors located well above the valence‐band edge of 3C–SiC. Photoluminescence investigation revealed that the Al‐ and B‐doped specimens exhibited emission profile below 2 eV, implying the existence of the acceptors.     

Development of a novel proton conducting fuel cell based on a Ni‐YSZ support

A new proton conducting fuel cell design based on the BZCYYb electrolyte is studied in this research. In high‐performance YSZ‐based SOFCs, the Ni‐YSZ support plays a key role in providing required electrical properties and robust mechanical behavior. In this study, this well‐established Ni‐YSZ support is used to maintain the proton conducting fuel cell integrity. The cell is in a Ni‐YSZ (375 μm support)/Ni‐BZCYYb (20 μm anode functional layer)/BZCYYb (10 μm electrolyte)/LSCF‐BZCYYb (25 μm cathode) configuration. Maximum power density values of 166, 218, and 285 mW/cm² have been obtained at 600°C, 650°C, and 700°C, respectively. AC impedance spectroscopy results show values of 2.17, 1.23, and 0.76 Ω·cm² at these temperatures where the main resistance contributor above 600°C is ohmic resistance. Very fine NiO and YSZ powders were used to achieve a suitable sintering shrinkage which can enhance the electrolyte sintering. During cosintering of the support and BZCYYb electrolyte layers, the higher shrinkage of the support layer led to compressive stress in the electrolyte, thereby enhancing its densification. The promising results of the current study show that a new generation of proton conducting fuel cells based on the chemically and mechanically robust Ni‐YSZ support can be developed which can improve long‐term performance and reduce fabrication costs of proton conducting fuel cells.     

Effect of thermal history on high‐valence chromium ion dissolution in merwinite (3CaO·MgO·2SiO2)

Solubility and local structure of transmission elements in calcium silicate compounds has not been well understood. We investigate the local structure of chromium ions dissolved in merwinite (3CaO·MgO·2SiO₂) of a monoclinic crystal structure. The acceptance of doping elements into merwinite has not been reported before. We found that chromium ions are soluble in merwinite in air and that chemical valence of the dissolved Cr ions varies with annealing temperature. The absorption edge in the x‐ray absorption near edge structure (XANES) of Cr‐doped merwinite indicated that octahedrally coordinated Cr³⁺ ions were mainly formed when annealed at 1673 K in air. A pre‐edge peak was also detected, indicating the existence of tetrahedrally coordinated high‐valence Cr ions. Conversely, through annealing of merwinite at 1123 K in air, tetrahedrally coordinated Cr⁶⁺ ions were found to be the main form of chromium. XANES spectra simulated by first‐principle calculations were used to explain the structural features in the observed spectra. We propose the coexistence of Cr³⁺ ions in octahedral Mg²⁺ sites and high‐valence Cr ions in tetrahedral Si⁴⁺ sites. In addition, a change in the chromium ion oxidation state in tetrahedral coordination sites was suggested by XANES spectroscopy of Cr‐doped merwinite synthesized at 1673 K and reannealed at 1123 K.     

Characterization of Magnesium‐Doped Hydroxyapatite Prepared by Sol‐Gel Process

Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca_10‐xMg_x(PO₄)₆OH₂) were synthesized using sol‐gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg⁺²) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as‐prepared powders had a specific surface area ranged between 6.37 and 27.60 m²/g.     

Thermal kinetics and phase stability of 8 mol% samaria doped zirconia nanopowders prepared via reverse coprecipitation

Nanocrystalline samaria (8 mol%) doped zirconium oxide (8SmSZ) was synthesized using reverse co-precipitation technique, the calcination temperature ranging from 873 K to 1273 K for 2 h. XRD structural analysis results confirm the tetragonal(t) nature of the synthesized 8SmSZ nanocrystalline powder. The calculated crystallite size of tetragonal zirconia calcined at 873 K is around 9.0±0.5 nm and with increase in calcination temperature the size increases to 16.0±0.8 nm (1273 K). Thermogravimetric-Differential thermal analysis (TG-DTA) was carried out to study the crystallisation kinetics and growth behaviour of the 8SmSZ. The activation energy for the crystallisation of tetragonal ZrO₂ formation in the 8SmSZ powder was found to be 308.1 kJ/mol by a non-isothermal DTA method. The growth morphology parameter was found to be n=2 indicating two-dimensional growth. The phase stability of the samples after annealing at 1573 K for 100 h was investigated by Raman spectroscopy and it was found that samaria doped zirconia exhibits better phase stability. These preliminary results confirmed the higher phase stability at elevated temperature thereby confirming its suitability in thermal barrier coating (TBC) applications.     

Emergence of defect fluorite structure in nano‐sized thoria through doping with some divalent transition‐metal ions

With the objective of incorporating some divalent transition‐metal ions in thoria and to comprehend its effect on the crystal structure, electronic as well as catalytic properties, Ni²⁺, Cu²⁺ and Cd²⁺ substituted thoria samples were synthesized by the epoxide gel method. Of the two concentrations investigated, 10 mol% of Ni²⁺, Cu²⁺, and Cd²⁺ could be substituted retaining the fluorite structure and phase separation into individual oxides was noticed for 15 mol%. The average crystallite size of thoria and 10 mol% substituted samples was 14 nm. Le‐Bail structural refinements of Powder X‐ray diffraction (PXRD) patterns indicated marginal increase in unit cell constant for the Cd²⁺ substituted sample and a decrease for Ni²⁺ and Cu²⁺ substituted samples. In addition to broadening of the band at around 460 cm^?1 (F_2g vibration of the fluorite), less intense band near 560‐590 cm^?1 emerged for all the transition‐metal ion‐containing samples in the Raman spectra implying the formation of oxygen defects. The absorption edge in the UV‐visible spectra moved toward higher wavelength for Cd²⁺, Ni²⁺ and Cu²⁺ containing samples as compared to pure thoria. In addition, d‐d transition was observable for Ni²⁺ and Cu²⁺ containing samples. By virtue of these changes in the electronic structure of transition‐metal ion‐containing samples, they were examined as catalysts for the degradation of aqueous Rhodamine‐6G (Rh‐6G) dye solutions under visible radiation.     

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

The semiconductors based on simple oxide have unique features with controllable electrical property by element doping. Y³⁺ doped NiO (Ni_1−xY_xO, x ≤ 0.01) and Mg²⁺ substituted Ni_0.995Y_0.005O (Ni_0.995−yY_0.005Mg_yO, 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.     

Thermoelectric Properties of Pb‐Doped BiCuSeO Ceramics

A high‐performance thermoelectric BiCuSeO oxyselenides has been prepared by a simple fabrication approach. Phase composition and microstructure analysis indicate that the obtained ceramic samples are almost BiCuSeO phase with plate structure. Our results show that Pb‐doped BiCuSeO bulks have good electrical conductivity, large Seebeck coefficient, and low thermal conductivity. A large power factor ~672 μ/Wm/K² at 573 K can be observed in the BiCuSeO ceramic by the 10% Pb doping, and the dimensionless figure of merit (ZT) can reach 0.95 at 873 K, which makes them promising candidates for thermoelectric applications.     

Preparation of Phase‐Pure K0.5Na0.5NbO3 Fine Powders by a Solid‐State Reaction at 625°C from a Precursor Comprising Nb2O5 and K,Na Acetates

Phase‐pure K_0.5Na_0.5NbO₃ (KNN) fine powders were synthesized via a solid‐state route from a homogeneous solid mixture. A colloidal dispersion comprising a mixed ethanol solution of potassium and sodium acetates and Nb₂O₅ fine particles was attrition milled and dried carefully to avoid water absorption. Two‐step calcination in air at 450°C and 625°C, each for 3 h, resulted in the phase‐pure KNN powders. The volume‐based median diameter of the final product was ca. 0.8 μm. Starting from the same precursors without dissolving the acetates, the phase‐pure KNN was never achieved even when the two calcination temperatures were increased to 550°C and 700°C, in spite of the same milling conditions. Key issues of eliminating second phases were (i) starting from a wet‐milled mixture with a single solution containing both of the A‐site species, and (ii) repeated wet milling of the reaction mixture to disintegrate reaction‐induced agglomerates. These enabled rapid nuclei growth from chemically interacted precursor prior to calcination, and short diffusion path due to repeated deagglomeration, excluding formation of off‐stoichiometric second phases. All these items were confirmed by different analytical tools, among others, thermo‐gravimetry and differential thermal analysis (TG‐DTA), particle size analyses, and XPS at various reaction stages. On the heating stage microscope, a shrinkage onset was observed at 850°C, that is, 150 K lower than that of conventionally prepared KNN, that is, via a solid‐state synthesis from carbonates by a two‐step calcination at 800°C and 750°C, for 4 h each. No second phase was observed after sintering up to 1100°C.     

Synthesis of a magnetically removable visible-light photocatalyst based on nickel-doped zinc ferrite

In this study, a facile method to synthesize magnetically removable visible-light photocatalysts based on nickel-doped zinc ferrites is presented. Ferrite semiconductor ceramics with the general formula Zn_1-xNi_xFe₂O₄ (0 ≤ x ≤ 0.5, Δx = 0.1) were prepared by high-energy ball milling followed by annealing at 873 K. X-ray diffraction analysis confirmed the spinel single-phase Fd-3m without secondary phases for all compositions. The slight decrease in lattice parameters confirmed the presence of Ni²⁺ ions in the crystal structure because Ni had a smaller ionic radius than Zn. Raman spectroscopy demonstrated that Ni²⁺ ions were distributed on both tetrahedral and octahedral sites, which increased the inversion parameter and affected the photocatalytic efficiency and ferromagnetism. Magnetic hysteresis loops suggested an increase in the specific magnetization as the doping content increased, enabling magnetic recovery and reuse of the photocatalyst in water remediation. Diffuse reflectance spectroscopy showed a reduction in the band gap values with increasing nickel content, which was attributed to forming a sub-level in the band structure in the presence of Ni²⁺. Photocatalytic tests revealed a degradation efficiency higher than 60%, confirming that the doped samples obtained by high-energy ball milling were highly efficient and easily removable photocatalytic materials.     

Improved Electrodes/Electrolyte Interfaces for Solid Oxide Fuel Cell by Using Dual‐Sized Powders in Electrolyte Slurry

The dense electrolyte film with the rough surfaces for solid oxide fuel cell (SOFC) was fabricated on NiO/yttria‐stabilized zirconia (YSZ) anode substrate by using dual‐sized YSZ powders without additional effort to roughen electrolyte film. The dual‐sized YSZ powders consisted of the fine YSZ powder and the coarse YSZ powder at different weight ratios. Incorporation of the coarse YSZ powder into the fine YSZ powder is in order to increase the surface roughness of electrolyte film, and the surface roughness obviously increased with the increase of coarse YSZ powder. The rough surfaces resulted in an enlargement of the electrochemical active area. It was found that electrode polarization was reduced evidently and cell electrochemical performance was enhanced, as the surface roughness increased. However, the excessive coarse YSZ powder was not beneficial for densification of electrolyte film and thus the open‐circuit voltage (OCV) was declined. The cell with 17 wt.% coarse YSZ powder in the electrolyte exhibited the best performance and the maximum power density was 1,930 mW cm^–2 at 800 °C.     

Nano–Nano Composite Powders of Lanthanum Zirconate and Yttria‐Stabilized Zirconia by Spray Pyrolysis

Powders composing of La₂Zr₂O₇ (LZ) and (Zr_0.8Y_0.2)O_1.9 (10YSZ) phases (volume ratio = 1:1) were synthesized by using a sol‐spray pyrolysis method. The effects of annealing temperature on the grain size and lattice parameter of the LZ–10YSZ powders were investigated. XRD results showed that the grain size of LZ and 10YSZ phases gradually grew from 10 to 95 nm and from 5 to 65 nm as the annealing temperature elevated from 900°C to 1200°C. The relative decreasing percentage of grain size comparing to that of the single‐phase LZ and 10YSZ powders were in the range 9%–36% and 37%–86%. The activation energy for grain growth of LZ and 10YSZ phases in the composite powders were 225 ± 12 and 382 ± 17 kJ/mol, which were 20% and 183% higher than that of the single‐phase counterparts. Obvious lattice contraction and lattice expansion for LZ and 10YSZ phases were observed at temperatures below 1100°C, respectively. SEM results revealed that LZ and 10YSZ phases were homogeneously distributed in the sintered bulk. The TEM results suggested that the grain growth was affected by the interaction on nanometer length scales of grain boundaries between LZ and 10YSZ phases in the composite.