Defect Fluorite Structure Research Articles

The influence of the elemental valence on the thermophysical properties of high entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings for thermal barrier application

Commercial yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are no longer sufficient for the stringent demands in the high operating temperature and excellent thermophysical properties of the high-performance gas turbines and aviation engines. High entropy ceramics, distinguished by their superior thermophysical properties, have risen as a potential substitute for TBCs. However, the realm of atmospheric plasma spraying (APS) in the creation of these advanced TBCs remains relatively unexplored. In this work, three distinct high-entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings were developed through the meticulous alteration of spraying power. The effects of spraying power on the microstructure, valence states of constituent elements and thermophysical properties of the coatings were deeply investigated. The results indicated that all the as-sprayed coatings exhibit a defect fluorite structure. Spraying power does have a significant impact on the thermophysical properties of the coatings. With the decrease in spraying power, the thermal conductivity of the coatings shows a progressive reduction, whereas the coefficient of thermal expansion (CTE) exhibits a gradual increase. This trend is closely related to valence states of constituent elements in the coatings. The resulting coating exhibits a low thermal conductivity of 0.54 W⋅m-1⋅K-1, a high CTE of 11.22×10-6·K-1 and a superior phase stability at elevated temperatures.

Influence of non-stoichiometric design concepts on the optical properties of Sm-doped Gd2Zr2O7 transparent ceramics

The concept of non-stoichiometric design, as a historically significant strategy in material design, plays a crucial role in the development and innovation of materials. Particularly in the domain of red-orange fluorescence, the importance of the rare earth Sm element has been increasingly emphasized. This study successfully prepared non-stoichiometric Gd2Zr2O7 transparent ceramics doped with Sm using combustion and vacuum sintering. X-ray diffraction analysis indicates that the obtained powders are composed of fine defect fluorite structure grains, while the final ceramics exhibit pyrochlore/defect fluorite phase. Initially, non-stoichiometric design optimizes the optical transmittance of ceramics. The maximum transmittance of the X = −0.1 ceramic exhibits the highest transmittance 82.4 % @ 1134 nm. Furthermore, photoelectrons captured by native defects energy levels can transfer to the Sm excited states, optimizing the fluorescence property of ceramics. The fluorescence intensity of the X = 0.8 ceramic is about five times that of the X = 0 ceramic.

Oxygen ion diffusion in RE3TaO7: Why long-range migration of O2− is prohibited in the defective-fluorite structure?

Oxides with low O2− lattice diffusion rate are critical for the development of topcoat materials for next generation thermal barrier coatings (TBCs) working at > 1600 °C to prevent the fast growth of thermally grown oxide (TGO) at the bondcoat/topcoat interface. Here we delve into a comprehensive analysis of the oxygen ion transport characteristics of the recently developed low-, medium- and high-entropy rare earth tantalates (RE3TaO7) for TBCs by a combination of impedance spectroscopy, 18O isotope diffusion tests and atomic-scale simulations. Results show that the RE3TaO7 series display remarkably low oxygen ion diffusion rate (> 3 orders of magnitude lower than the state-of-the-art topcoat material yttria stabilized zirconia, YSZ) despite the presence of abundant oxygen vacancies in the structure. Molecular dynamic (MD) simulations combined with first principles calculations reveal that oxygen ions are strongly trapped by the potential well at the Ta-Ta edge in the tantalates. In addition, the high electrostatic potential (EP) surrounding oxygen vacancies and the high diffusion barriers between rare earth elements also impede oxygen ion diffusion. With low oxygen ion diffusion rate, along with exceptional thermal and mechanical properties reported previously, RE3TaO7 are promising topcoat materials for next-generation TBCs working at higher temperatures. Moreover, this study also provides valuable insights for understanding the O2− lattice diffusion behaviour in RE3TaO7 with a defective fluorite structure, which may benefit the exploration of oxide-ion conductors.

Stable preparation of defective fluorite structure high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2Zr2O7 ceramic powders by molten salt synthesis

Rare earth zirconate ceramic has been considered as one of the potential thermal barrier coating materials to replace 6–8% YSZ material (6–8% yttrium oxide stabilized zirconia), because of its low thermal conductivity and good high temperature phase stability. However, there is a problem that the coefficient of thermal expansion does not match the matrix. In this paper, rare earth high entropy zirconate ceramic powder with defective fluorite structure was prepared by molten salt synthesis(MSS). The results show that the reaction temperature and the ratio of reactants to molten salt will affect the synthesis effects. With the action of the high entropy effect, the synthesized ceramic powder has low thermal conductivity, improved thermal expansion coefficient and high infrared reflectivity.

Improved resistive switching behavior of defective fluorite structured Sm2Ce2O7 thin film prepared by RF sputtering

The Al/Sm2Ce2O7/ITO (Al/SCO/ITO) structure resistive random access memory (RRAM) was prepared using RF magnetron sputtering, and its resistive switching (RS) behaviors were systematically investigated. The memory exhibited a high switching cycle of 1031, along with set/reset voltages of −1.55/0.53 V and a Ron/Roff ratio exceeding 102. This high performance can be attributed to the presence of intrinsic oxygen vacancies in the defective fluorite structure, accounting for 34.44 % of the vacancies. This vacancy percentage can be increased to 41.97 % by simultaneously transforming Ce4+ to Ce3+ ions through annealing treatment, thereby releasing additional oxygen vacancies. Despite this increase, there remains a sufficient window (Ron/Roff > 10) to distinguish between the high-resistance state (HRS) and low-resistance state (LRS) of the SCO device. Furthermore, the device, when subjected to post-metal annealing (PMA), exhibits a high endurance of up to 1815 cycles, a set/reset voltages of −2.19/1.31 V, a Ron/Roff ratio of >10, and a retention time of over 104 s at 25 °C and 85 °C. However, it is important to note that PMA-treated device requires a higher forming voltage due to the formation of a thicker AlOx layer. This study highlights the potential of Al/SCO/ITO memory devices for RRAM applications.

Low-temperature properties of magnetically frustrated rare-earth zirconates A 2Zr2O7

Rare-earth A 2Zr2O7 zirconates have attracted considerable attention of the scientific community for their complex magnetic, electronic and material properties applicable in modern technologies. The light rare-earth members of the series, crystallising in the pyrochlore variant of cubic crystal structure, have been studied in detail. The heavier A 2Zr2O7 compounds have been investigated mainly from the material properties viewpoint, focussing on their thermal properties and stability at high temperature and pressure. Low-temperature studies were mostly missing until recently. We present the low-temperature magnetic and thermodynamic properties of A 2Zr2O7 with A = Y, La, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu, well covering the whole series, newly synthesised by high-temperature sintering and melting methods. X-ray diffraction reveals and confirms the ordered pyrochlore structure in the light members, the disordered cubic structure of the defect-fluorite type in A 2Zr2O7 with A = Y, Gd–Yb, and finally the lower symmetry rhombohedral structure in the end-member Lu2Zr2O7. The specific heat of the investigated compounds is dominated by a low-temperature anomaly associated with magnetic ordering: long-range in light rare-earth zirconates; and short-range in heavier members. The effective magnetic moment in the studied compounds, determined by fitting the magnetisation data to the Curie–Weiss formula, is in good agreement with the expected value of the A 3+ free ion. The magnetic properties have been revealed to be strongly influenced by the geometric frustration of the magnetic moments of both the pyrochlore structure, as well as the face centred cubic lattice created by the cations of the defect-fluorite structure, but connected also to intrinsic atomic disorder. The experimental results are discussed in the framework of previous studies on A 2Zr2O7 zirconates, as well as other A 2 B 2O7 compounds.

Comparative study on the synthesis and characterization of Gd2Zr2O7 nanoparticles by mechanical milling and Co-precipitation techniques

Gadolinium Zirconate nanoparticles were synthesized by Co-precipitation and Ball milling techniques. In this study, the effect of the synthesis technique and calcination temperature on the structural, morphological and thermal properties were investigated. The thermal properties examined showed that the GZ nanoparticles obtained from CP technique suffered two-fold weight loss as compared to BM technique. The SEM results revealed the formation of agglomerated particles. However, TEM results confirms the formation of nanoparticles of 10.5 nm and 8 nm by BM and CP techniques respectively. GZ particles obtained through CP technique showed better uniformity of particle size over BM technique. The functional groups of the nanoparticle were studied using FT-IR spectroscopy analysis. The XRD results confirm the formation of defect-fluorite structure and pyrochlore structure for the samples calcined at 1100 °C and 1400 °C (BM) respectively. The formation of the corresponding structures was further confirmed by Raman Spectroscopy. The thermal conductivity of the nanoparticle produced by ball milling and co-precipitation technique is almost same. As compared to NiCrAlY and uncoated substrate materials, the micro hardness of the GZ coatings has the maximum hardness of 594.6 HV, indicating the improved hardness behavior of TBC system.

Effects of Gd3+ doping on phase compositions, mechanical properties and thermophysical properties of (Yb1-xGdx)4Hf3O12 ceramics

A series of (Yb1-xGdx)4Hf3O12 (x=0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by a solid-state reaction at 1600 °C for 10 h. The phase compositions, microstructure, mechanical properties and thermophysical properties of (Yb1-xGdx)4Hf3O12 ceramics were investigated. Yb4Hf3O12 exhibited a δ-phase structure, while Gd3+ doped Yb4Hf3O12 had a defect fluorite structure. The Gd3+ doped Yb4Hf3O12 showed higher Vicker's hardness, fracture toughness and Young's modulus compared to Yb4Hf3O12. The thermal conductivities of (Yb1-xGdx)4Hf3O12 ceramics firstly decreased with increasing Gd3+ doping, but subsequently increased with further Gd3+ doping. The (Yb0.7Gd0.3)4Hf3O12 exhibited the lowest thermal conductivity of 1.33 W m-1·K-1 at 1200 °C. The thermal expansion coefficients (TECs) of Gd3+ doped Yb4Hf3O12 were higher than that of Yb4Hf3O12. The (Yb0.7Gd0.3)4Hf3O12 showed promising comprehensive properties, suggesting that it could be a potential candidate material for thermal/environmental barrier coatings (T/EBCs).

Resistance of (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 top-coat material in thermal/environmental barrier coatings to calcium-magnesia-alumina-silicon attack at 1300 °C and 1500 °C

Rare earth elements (Dy, Ho, Er, Tm, and Lu), characterized by low-diffusivity in silicate melts, were designed as defect-fluorite structure high-entropy material (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 to determine its resistance to calcium-magnesia-alumina-silicon (CMAS) attack. The results indicate that corrosion reactions preferentially crystallize anorthite and garnet phases in the front of molten CMAS at 1300 °C, which alleviates rapid infiltration of CMAS. The reaction between the melt and (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 forms mixture layers comprising apatite and fluorite phases at 1500 °C, which are accompanied by the prompt exhaustion of CMAS. The capability of intaking RE determines the formation mechanisms of apatite with two different structures. The study reveals that the high-entropy material effectively resists molten CMAS attack at 1300 °C; however, its effectiveness in preventing rapid corrosion decay diminishes at 1500 °C. Factors affecting reaction control were discussed at each condition to elucidate the interactions between the multi-cation hafnate material and silicate deposits. This study represents a significant stride towards advancing high-entropy hafnate thermal barrier coating material applications in aerospace engineering.

Magnetic frustration in rare-earth zirconates A2Zr2O7, the case of laser heated pedestal method synthesised A = Er, Tm, Yb, and Lu single crystals

Heavy rare-earth A2Zr2O7 zirconates have been studied for their high application potential, including thermal barrier coating, radiation waste storage, or solid oxide fuel cells. However, previous investigations have focused mostly on the high-temperature properties of polycrystalline samples. The low-temperature properties, important for a full understanding of these materials, remains understudied. We have newly synthesised good-quality single crystals of A2Zr2O7 with A = Er, Tm, Yb, and Lu using the laser heated pedestal method and have characterised them by means of X-ray diffraction, magnetisation, and specific heat measurements. The first three members crystallise in a cubic disordered defect-fluorite structure. Lu2Zr2O7 adopts lower-symmetry rhombohedral structure. Similar magnetic properties of all magnetic zirconates were observed at low temperature. In the unperturbed paramagnetic state, they follow the Curie-Weiss law with an effective magnetic moment close to the respective A3+ free ions. The negative paramagnetic Curie-Weiss temperature, in the case of A = Yb member highly negative, strongly suggests an antiferromagnetic ordering in the compounds. Below 30 K, the magnetic response becomes non-linear in the applied magnetic field, suggesting magnetic correlations between rare-earth moments or/and crystal field effects. Finally, at lowest measured temperature, Er2Zr2O7 and Yb2Zr2O7 members reveal a well-pronounced anomaly in specific heat at 0.9 and 1.5 K, respectively. The specific heat anomaly shifts to higher temperature in an applied magnetic field, suggesting ferromagnetic correlations – in contradiction to the negative Curie-Weiss temperature. We discuss these observations in the framework of freezing of magnetic moments on a disordered geometrically frustrated lattice. In contrast, the low-temperature properties of Tm2Zr2O7 are dictated mostly by its crystal electric field; a crystal-field-singlet ground state which does not provide degrees of freedom for a spin-freezing is proposed. No clear low-temperature anomaly in specific heat is observed down to 0.4 K for the A = Tm member. Lu2Zr2O7 does not bear any magnetic moment, therefore no magnetic signal was observed in any measured data. The results are discussed in the framework of heavy rare-earth A2B2O7 oxides and other magnetically frustrated systems.

He2+ irradiation response of structural evolution at different depths of MgO-Nd2(Zr1-xCex)2O7 composite ceramics used for inert matrix fuel

This paper reported the irradiation response of a 55 wt.% MgO-45 wt.% Nd2(Zr1-xCex)2O7 (abbreviated to M-NZCx, x = 0, 0.3 and 1) composite ceramics used as candidate inert matrix fuel under 500 keV He2+ ions with fluence of 1 × 1016–5 × 1017 ions/cm2. The irradiation-induced lattice expansion, amorphization of MgO and NZCx phases and order-disorder transition of Nd2(Zr1-xCex)2O7 pyrochlore were systemically explored via GIXRD, Raman and TEM techniques. And the detailed irradiation response at different depths of the typical M-NZC0.3 sample was especially investigated via GIXRD and TEM. The results showed that the lattice expansion ratios (Rs) of MgO (M), ordered pyrochlore (P) and disordered defect-fluorite (F) structures of NZCx pyrochlore in the samples under the same dose of He2+ irradiation were regular, which were ranged as the following order: RsM < RsP < RsF. And there was a belt-shaped damage aggregation zone located near interphase boundary at the maximum damage depth of M-NZC0.3 sample, which could be explained by the defect-absorption of boundary. And this defect-absorption of boundary was also found at any depth of M-NZC0.3 sample. This work systematically analyzed α-decay irradiation response of different phases in M-NZCx composite ceramics applying for inert matrix fuel.

Effect of the high temperature phase transition on the tribological behavior of atmospheric plasma sprayed AlCoCrFeNi-Bi2O3 coating

Owing to the brittleness of the body-centered cubic (BCC) structure and lack of self-lubrication, plasma-sprayed AlCoCrFeNi high-entropy alloy (HEA) coatings undergo severe abrasive wear, resulting in high friction and wear. In this study, the substrate surface temperature was increased (800 °C) to promote the phase transition from BCC to ductile FCC during spraying. As a result, the prepared AlCoCrFeNi HEA coating contained BCC and FCC phases, exhibiting a higher adhesive strength, lower friction coefficient and wear rate at room temperature (RT)–800 °C. In addition, the elevated substrate surface temperature enabled the transition of the low-temperature stable phase α-Bi2O3 to the high-temperature stable phase δ-Bi2O3. δ-Bi2O3 promoted the formation of low shear strength planes owing to its low interaction parameter and defect-fluorite structure with 25 % anionic vacancies similar to that of the Magnéli phase, which facilitated friction reduction in a wide temperature range. This study confirms that δ-Bi2O3 can effectively improve the anti-wear performance of the AlCoCrFeNi-Bi2O3 coating at RT, 200, 600 and 800 °C. However, at 400 °C, the low melting point and soft nature of the Bi2O3 weakened the mechanical strength of the coating and inhibited the construction of a solid and tough tribo-layer, resulting in a relatively high wear rate for AlCoCrFeNi-Bi2O3 coating. At 800 °C specifically, under the thermal coupling effect, δ-Bi2O3 migrated and aggregated on the worn surface with the oxidation product Al2O3 of the AlCoCrFeNi HEA matrix, and jointly promoted the formation of a compact and smooth tribo-layer with lubricating capability, which not only effectively reduced friction but also inhibited wear.

Effect of multi-component at the A site on the phase and sintering resistance of high entropy rare earth zirconates

A series of high entropy rare earth zirconate ceramics, (5A0.2)2Zr2O7, with single- or dual-phase structures were synthesized using the solid-state reaction method. The cations at the A site varied in terms of average ionic radius RA, atomic mass MA, radius (size) disorder δR, and mass disorder δM. Our results demonstrate that increasing the structural disorder degree promotes the transition from an ordered pyrochlore structure to a defective fluorite structure, and leads to poor sintering resistance. The structural disorder degree of the high entropy zirconates could be increased by decreasing the ionic radius ratio RA/RZr, increasing the size disorder δR and introducing Ce4+ at the A site. Meanwhile, large size disorder leads to strong partitioning of rare earth ions and deviation of the lattice constant from the predicted value. The presence of Ce4+ ions at A site could significantly increase the structural disorder degree and promote the sintering process, and the underlying mechanisms are proposed and discussed.

Formation of single-phase multicomponent zirconate with colossal atomic radius difference via reactive flash sintering

In this study, multicomponent rare-earth zirconate ceramics (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 and (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7 were synthesized via conventional sintering and reactive flash sintering, respectively. Single-phase (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 ceramics, with the defect fluorite structure, were successfully obtained via conventional sintering and reactive flash sintering, while secondary phase segregation and precipitation were observed only in conventionally-sintered (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7 ceramics. This study proposes that the critical electric field of reactive flash sintering introduces defects to soften the lattice, which not only improves the mass transportation, but also relieves the lattice stress induced by the atomic radius difference, resulting in the single-phase defect fluorite structure of (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7. Thus, reactive flash sintering is an efficient route for synthesizing and developing novel multicomponent oxides that cannot be synthesized via conventional sintering due to pronounced lattice stress.

Effects of Gd3+ substitution on the structure, photoluminescence, scintillation, and thermometric features of Pr3+:Lu2Zr2O7 phosphors

AbstractIn this study, it is shown how the photoluminescence, scintillation, and optical thermometric properties are managed via the introduction of Gd3+ ions into Pr3+:Lu2Zr2O7. Raman spectra validate that partial replacement of Lu3+ with Gd3+ can promote the phase transition of Lu2Zr2O7 host from the defective fluorite structure to the ordered pyrochlore one. Upon 289 nm excitation, all the samples emit the 483 (3P0 → 3H4), 581 (1D2 → 3H4), 611 (3P0 → 3H6), 636 (3P0 → 3F2), and 714 nm (3P0 → 3F4) emissions from Pr3+ ions, which are enhanced with the addition of Gd3+ ions due to the modification of crystal structure. Dissimilarly, the X‐ray excited luminescence spectra consist of a strong emission located at 314 nm from Gd3+ ions (6P7/2 → 8S7/2), together with the typical emissions from Pr3+ ions, which exhibit different dependences on the Gd3+ concentration. When the luminescence intensity ratio between the 3P0 → 3H6 (611 nm) and 1D2 → 3H4 (581 nm) transitions is selected for temperature sensing, Pr3+:(Lu0.75Gd0.25)2Zr2O7 shows the optimal relative sensing sensitivity of 0.78% K−1 at 303 K, which is higher than that of the Gd3+‐free sample. Therefore, the developed Pr3+:(Lu, Gd)2Zr2O7 phosphors have the applicative potential for optical thermometry, X‐ray detection, and photodynamic therapy.

Development, characterization, and properties of LnSmZr2O7 (Ln = Dy, Ho, Yb) defect fluorite functional ceramics

LnSmZr2O7 (Ln = Dy, Ho, Yb) functional nanoceramics are prepared through a citrate-nitrate auto-combustion method. High-density pellets using the powder are obtained by sintering at 1530 °C for 2 h. The defect fluorite structure of the powder and sintered samples is established using XRD and Raman analysis. The morphology of the powder analyzed using Transmission Electron Microscopy revealed the nanocrystalline nature of the combustion powder. The microstructure of the sintered sample analyzed using Field emission Scanning Electron Microscopy showed increased grain growth with larger cationic substitution. LnSmZr2O7 (Ln = Dy, Ho, Yb) have an indirect-allowed optical wide band gap and exhibit photoluminescence due to intrinsic defect structure. LnSmZr2O7 (Ln = Dy, Ho, Yb) are pure oxide ion conductors in the temperature range from 400 °C to 900 °C, with conductivity values of 0.89 × 10−3 S/cm, 0.72 × 10−3 S/cm and 0.60 × 10−3 S/cm, respectively, at 900 °C.

Thermo-physical properties, morphology and thermal shock behavior of EB-PVD thermal barrier coating with DLC YbGdZrO/YSZ system

(Yb0.1Gd0.9)2Zr2O7 (YbGdZrO) rare earth modified zirconate ceramics is one of the novel thermal barrier coatings (TBCs) materials which has attracted much attention in recent years and is suitable for higher temperature applications. YbGdZrO ceramic powders gained from solid-phase synthesis show a single defect fluorite structure. After calcined at 1723 K upon 400 h, whose powder does not form any new phases and exhibit outstanding thermal durability. The thermal expansion coefficient of YbGdZrO ceramics with the elevated temperature to 1573 K is attained to 10.76 × 10−6 K−1, which is slightly smaller than that of Gd2Zr2O7 (GZO) material (10.98 ×10−6 K−1) at the same temperature. The arithmetic mean of coefficient of thermal diffusion of YbGdZrO bulks measured at 1273 K is 0.385 mm2/s, that seems to be equivalent to that of GZO ceramics (0.388 mm2/s, 1273 K). The X-ray diffraction feature peaks of electron beam physical vapor deposition (EB-PVD) YbGdZrO ceramic coatings almost resemble to its ingot, except that the crystal face indices of their two strongest peaks are different. The pyramid-like shape can be scrutinized on top tip of columnar grain of the as-deposited YbGdZrO ceramic layer, which is associated to the cubic lattice in the fluorite structure. After 3000 cycles of flame thermal shock, the upper half of the coated sample surface occurs light green. While the closer is the position to edge of the specimen, the more obvious is the color. In addition, many small black spots with disorderly distribution are observed on the coating surface. A large number of irregularly distributed and cross-linked micro-cracks are displayed on the surface of YbGdZrO ceramic top layer as well as the averaged width of these micro-cracks is determined to be ∼8.523 µm. Although the ceramic coating appears to have a small number of layered exfoliation, the chemical composition of the exposed region still contains only elements of Yb, Gd, Zr and O. It does not stretch to either interface of double-ceramic-layer (DCL) YbGdZrO/YSZ or interior of YSZ ceramic coating.

Preparation and Thermophysical Properties of New Multi-Component Entropy-Stabilized Oxide Ceramics for Thermal Barrier Coatings

Five kinds of multi-component entropy-stabilized oxide ceramics were prepared by a solid-state reaction method for thermal barrier coatings, namely La0.125Y0.125Yb0.125Gd0.125Zr0.5O1.75 (LaYYbGdZr), Y0.125Yb0.125Gd0.125Ta0.125Zr0.5O1.875 (YYbGdTaZr), La0.1Y0.1Yb0.1Gd0.1Ta0.1Zr0.5O1.85 (LaYYbGdTaZr), Y0.125Yb0.125Gd0.125Ta0.125Hf0.25Zr0.25O1.875 (YYbGdTaHfZr), and La0.1Y0.1Yb0.1Gd0.1Ta0.1Hf0.25Zr0.25O1.85 (LaYYbGdTaHfZr). Many properties of the materials were studied, such as their microscopic morphology, crystal structure, thermophysical properties, and ablation resistance. The results show that the oxide ceramics synthesized in this paper have a uniform single-phase defect fluorite structure, and can still maintain this structure after high-temperature treatment at 1500 °C. The YYbGdTaHfZr coatings had the lowest thermal conductivity (0.61~0.89 W·m–1·K–1), which was much lower than that of YSZ. The ceramic blocks also exhibited excellent thermal expansion properties. The thermal expansion coefficient of LaYYbGdTaZr could reach 11.09 × 10−6 K−1 (1400 °C), which was slightly higher than that of 8YSZ (11.0 × 10−6 K−1). The antioxidant ablation results proved that the YYbGdTaHfZr coating showed the best heat-insulating property. All the results showed that the YYbGdTaHfZr coating is a promising thermal barrier coating.

Unveiling the underlying mechanism of unusual thermal conductivity behavior in multicomponent high-entropy (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xCex)2O7 ceramics

Previously, the research on thermal conductivity of ceramic thermal barrier coatings mainly focused on phonon and photon thermal conductivity (thermal radiation effect). However, electrical conductivity is remarkable in some systems. Hence, the contribution of phonon, photon and electronic heat conduction to thermal conductivity of high-entropy systems was evaluated in this study. The (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xCex)2O7 (x = 0–0.5) high-entropy ceramics with single defective fluorite structure were successfully prepared via a solid reaction method. Below 600 °C, the thermal conductivities decrease with increasing temperature for x = 0.1–0.5 components, then reveal a drastic temperature dependent increase. Moreover, the composition dependent thermal conductivities are also unusual based on the conventional phonon thermal conduction mechanism. The increased electronic thermal conductivity, improved photon thermal conductivity (at high temperatures) and reduced phonon-grain boundary scattering should be responsible for the unusual thermal conductivity behavior. This can be verified by the significantly increased electrical conductivity, optical transmittance and grain size, as well as reduced emissivity for (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xCex)2O7 high-entropy ceramics. The present study also broadens the way to investigate the thermal conductivity of ceramic thermal barrier coatings, and is helpful to design thermal barrier coatings with low thermal conductivity.

Structural analysis and properties of novel Terbium Samarium Zirconate functional ceramic

Synthesis and characterization of Terbium Samarium Zirconate (TbSmZr2O7) is reporting for the first time. XRD analysis along with Raman spectroscopy revealed that citrate-nitrate combustion synthesized TbSmZr2O7 powder and sintered sample crystallize in defect-fluorite structure with Fm3‾m space group. This composition lies at the pyrochlore-defect fluorite phase boundary. TEM analysis showed that the powder particles are in size range between 3 nm and 9 nm. FESEM image showed a well-sintered pellet surface with a grain size distribution between 0.1 μm and 2 μm. TbSmZr2O7 has an optical band gap of 1.66 eV and has an indirect allowed mechanism of optical transition. Due to intrinsic defect structure, TbSmZr2O7 exhibits photoluminescence with excitation bands at 270 nm and 313 nm and emission bands at 364 nm and 400 nm. Impedance spectroscopic analysis established that from 400 °C to 900 °C TbSmZr2O7 is a pure oxide ion conductor with a conductivity value of 1.9 × 10−3 S/cm at 900 °C.