CeO2 Buffer Layers Research Articles

Surface-to-bulk synergistic modification enables stable interface of Ni-rich oxide cathode for all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) are supposed to a highly forward-looking battery technology by reason of their conspicuous energy density and excellent safety. Ni-rich layered oxide cathodes have been extensively studied in ASSLB systems with sulfide electrolytes owing to their high voltage and preeminent specific capacity. However, the electrochemical performance of ASSLBs is severely degraded due to the interfacial physical contact failure, space charge layer effect, and chemical/electrochemical side reactions between sulfide electrolytes and Ni-rich oxide cathodes. In this work, the surface of LiNi0.92Co0.04Mn0.04O2 (NCM92) is coated with a nano-level CeO2 buffer layer and is simultaneously doped with Ce element (NCM92–1%Ce) by one-step wet chemical method. Ce doping is beneficial for maintaining structural stability and suppressing irreversible phase transition. The CeO2 buffer layer can efficaciously avoid the oxidation and decomposition phenomenon at the interface between NCM92 and sulfide electrolyte. As expected, NCM92–1%Ce cathode shows the discharge specific capacity of 141.46 mAh g−1 after 80 cycles at 0.2C with 79.32% capacity retention rate, which is much higher than that of the unmodified NCM92 cathode. The results indicate that the surface-to-bulk synergistic modification strategy can successfully improve the structure toughness and interface stability of Ni-rich oxide cathode for ASSLBs with sulfide electrolytes.

MOCVD deposited double-sided CeO2 buffer layer for YBCO superconducting film grow on R-plane Al2O3 substrate

Double-sided CeO2/YBCO films were grown on the double-sided polishing R-plane Al2O3 substrate using MOCVD technology. The effects of deposition parameters of the MOCVD setup on the structural orientation and surface morphology of CeO2 buffer layers grown on sapphire substrates were investigated. A series of CeO2 buffer layers were prepared by varying the substrate temperature and oxygen flow rate. The results show that when the substrate temperature is lower than 750 °C and the oxygen flow rate is lower than 400 sccm, CeO2 films is grown in a mixed (00l) and (111) orientations, and when the substrate temperature is 750 °C-840 °C and the oxygen flow rate is higher than 400 sccm, the CeO2 films are grown with a single (001) orientation. When the deposition temperature was 800 °C and the oxygen flow rate was 800 sccm, the CeO2 buffer layer structure had the best orientation with double-sided ω-scan FWHM of 0.019° and 0.02°; the FWHM of double-sided Ф-scan were 1.8° and 1.7°; the RMS roughness on both sides measured by AFM were 1.28 nm. YBCO films grown on this buffer layer have good c-axis epitaxial orientation, and the test results of the pole figure show an in-plane rotation of 45° between YBCO and CeO2 lattices. Thus, the obtained YBCO film has a critical current density of 2 MA/cm2, indicating that the films can be prepared to meet the needs of microwave devices using R-plane Al2O3 substrates.

Development of an efficient double absorber CIGSSe/perovskite solar cell with the combination of experimental data of Mg-doped CeO2 buffer layer

In this work, we developed a high-efficiency CIGSSe/perovskite photovoltaic cell with a combination of Mg-doped CeO2 buffer layer nanomaterials. Initially, Mg-doped CeO2 nanomaterials synthesized by the co-precipitation technique. The phase formation and hexagonal structure of CeMgO2 nanomaterial have been confirmed by X-ray diffraction (XRD). The XRD pattern has also been examined the lattice parameters constant of the pure and Mg-doped CeO2 nanomaterials. The morphology, average particle size, and surface qualities have been seen in scanning electron microscope (SEM) images. The optical properties are calculated using ultraviolet–visible (UV–Vis) spectrophotometry, and the electrical properties are calculated using Hall Effect measurements. The optical properties showed that the CeMgO2 nanomaterials' transmittance in the visible section increased from 89 to 98%, while their absorbance and reflectance decreased. Similarly, the optical energy bandgap improved from 3.578 to 3.865 eV, but the Urbach energy decreased from 0.251 to 0.115 eV with the change in the Mg-compositions. The rise in Mg-compositions causes an increase in defect quantity, which reduces DC and AC conductivity. The deviations of defect concentration with Mg-compositions were also observed in Photoluminescence (PL) element analysis. Further, with the use of experimental properties of Mg-doped CeO2 nanomaterials, we proposed a high-efficiency, eco-friendly, and flexible (SLG/Al/ZnMgO:Al/CeMgO2/CIGSSe/perovskite(MA-FA-Pb-Br-I)/Mo) solar cell. The proposed solar cell would absorb the bulk of ultraviolet (UV) light and improve photovoltaic parameters such as external quantum efficiency (EQE), efficiency (η) = 29.63%, short-circuit current density (JSC) = 40.25 mA/cm2, open-circuit voltage (VOC) = 855.6 mV, and fill factor (FF) = 86.02%.

Flexible self-powered DUV photodetectors with high responsivity utilizing Ga2O3/NiO heterostructure on buffered Hastelloy substrates

In this research, β-Ga2O3/NiO heterostructures were grown directly on CeO2 buffered Hastelloy flexible substrates. With pulsed laser deposition under high temperatures, as-grown β-Ga2O3 and NiO thin films have a preferred out-of-plane orientation along the ⟨−201⟩ and ➎111➉ directions. This is due to the ideal epitaxial ability of the CeO2 buffer layer, which serves as a perfect template for the epitaxial growth of single-oriented NiO and β-Ga2O3 by creating a constant gradient from CeO2 (2.7 Å along ➎001➉) to NiO (2.9 Å along ➎110➉), and eventually to β-Ga2O3 (3.04 Å along ➎010➉). The Hastelloy substrates endow photodetectors with good deformability and mechanical robustness. Moreover, owing to the type-II band alignment of β-Ga2O3/NiO heterostructures, the photodetectors have a good photocurrent at zero bias under 284 nm of light illumination. In addition, the photocurrent is significantly higher than when using an analogous heterostructure (as described in some previous reports), because the β-Ga2O3 and NiO thin films are crystalized along a single orientation with fewer defects.

Revealing intrinsic electro-optic effect in single domain Pb(Zr, Ti)O3 thin films

We deposited polar-axis-oriented tetragonal and rhombohedral single domain Pb(Zr, Ti)O3 (PZT) films on CaF2(100) substrates by inserting SrRuO3 (SRO)/LaNiO3 and SRO/SrTiO3/TiO2/CeO2 buffer layers. Both PZT films grew epitaxially and had a (001)- and (111)-domain with the remnant polarization and piezoelectric constant comparable to the theoretical values of PZT single crystals having the same compositions. The electro-optic (EO) response of the fabricated PZT films was constant with respect to the DC electric field and increased linearly with an increasing AC electric field, thus representing a typical linear EO response in single domain ferroelectrics. The measured EO coefficients were larger than the value for a single crystal of PbTiO3, i.e., one of the end members of PZT, but smaller than the values reported for polycrystalline and epitaxial PZT films with multiple domains. These findings show that the intrinsic EO effect is enhanced in PZT, which is similar to the enhancement seen in the dielectric and piezoelectric constants. Moreover, most of the reported EO response in PZT films is supported by additional extrinsic contributions.

The role of texturing and thickness of oxide buffer layers in the superconducting properties of Fe(Se,Te) Coated Conductors

In this paper the roles of texturing and thickness of different buffer layers employed in the fabrication of Fe(Se,Te) coated conductors are studied. Fe(Se,Te) thin films were deposited either on rolling assisted biaxially textured substrates substrates with highly textured CeO2 buffer layer and on HASTELLOY® C276 substrates with a randomly oriented native oxide grown through different oxidizing processes. It was found that the buffer layer has to be both thick enough to block Ni interdiffusion from the metallic tape to the Fe(Se,Te) overlayer, and textured enough to ensure good in-plane alignment of the superconducting film, and consequently good critical current densities (Jc). The best results in terms of critical temperature (Tc) and critical current were obtained using a highly textured 350 nm thick CeO2 buffer layer, but a fairly good Jc of 1.2 104 A cm−2 in self field at 5 K was also obtained using an HASTELLOY® C276 substrate with a 400 nm thick randomly oriented native oxide. The obtained results indicate that the superconducting properties of the Fe(Se,Te) coated conductors are determined by a trade-off between degree of texturing of the substrate and inhibition of Nickel interdiffusion.

In Situ EBSD Study of Stable Cube Texture in an Advanced Composite Substrate Used in YBCO-Coated Conductors.

Advanced Ni8W/Ni12W/Ni8W alloy composite substrates used in YBCO-coated conductors with a strong cube texture and high yield strength have been fabricated, and a CeO2 buffer layer film was successfully deposited on the composite substrates. Through in situ tensile testing coupled with electron backscattered diffraction (EBSD) analysis, the stability of the cube texture of Ni8W/Ni12W/Ni8W alloy composite substrates has been investigated. The stress-strain curve shows that the yield strength (at 0.2% strain) of the composite substrates exceeds 250 Mpa. The orientation of grains and boundaries on the surface of the substrates was almost unchanged, while the strain exceeds 0.2%, which indicated that the composite substrates are adequate for depositing buffer layers and YBCO layers by the reel-to-reel process.

Interfacial Engineering Enabled Novel Bi-Based Layered Oxide Supercells with Modulated Microstructures and Tunable Physical Properties

Two-dimensional layered materials hold great significance to fundamental scientific research and future nanoscale device applications. Besides the well-studied graphene and dichalcogenides, oxide-based layered materials are another family attracting significant research interests, for example, the Bi-based Bi3Fe2Mn2O10-δ layered supercell (called BFMO322 SC) structure. BFMO322 SC is an excellent room-temperature multiferroic material, but its growth mechanism is unclear. In this work, Bi2Fe1–xMnxO6 thin films with different Fe/Mn molar ratios were deposited on CeO2 buffer layers by pulsed laser deposition. By varying the Fe/Mn molar ratios, it has been determined that Mn can favor the growth of Bi-based layered structures, while Fe cannot facilitate the growth. A series of novel layered supercell structures can be obtained by manipulating the growth kinetics at the substrate/film interface, as achieved by precisely controlling the growth conditions. More interestingly, the magnetization and optical band g...

Mechanical Damage of YBa2CU3O7-Coated Conducting Film Caused by Its CeO2 Interface with Defects

YBa2Cu3O7 (YBCO) multilayer coating conductors are the second generation superconductor wires. The interface structure plays an important role in the performance of the material, especially that between the superconducting layer and the CeO2 buffer layer. The YBCO/CeO2 interface is not only very critical on the atomic scale for effectively modulating the polycrystalline structure of YBCO, but also, as weak connection on the macro level, profoundly affect macro physical properties of the whole film, for example, mechanical toughness. Generally, most defects at the YBCO/CeO2 interface are generated during the fabrication, and further develop when the film is wound or in the process of current carrying. These defects, at different level, lead to mechanical damage even under simple deformations such as tension and bending. In this work, by way of atomistic computer simulations with the molecular dynamics (MD), a two-dimensional YBCO/CeO2 interface atomic model was developed and validated. On this interface model, the damage propagation on the atomic-scale and further analysis with stress and potential energy especially affected by the YBCO/CeO2 interface with/without defects under the tension and bending have been comprehensively investigated. As a result, we not only visualized the simulated damage process and route on the YBCO/CeO2 interface, but also more importantly, combined with the variation of macro properties, deeply analyzed the damage mechanism caused by the interface and its defects.

Enhancement of the in-field critical current density of trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films by annealing of CeO2 buffered R-Al2O3 substrates

We investigate the superconducting properties of (Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films on as-grown and annealed (600 °C–1000 °C) CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). The annealing was found to improve the crystallinities of not only the CeO2 buffer layers but also the (Y,Gd)BCO films. Although the anneal had no apparent effect on the pinning centers of the (Y,Gd)BCO films, the in-field Jc of the (Y,Gd)BCO films grown on the CeO2 buffered substrates improved with increasing annealing temperature. The present results are discussed in terms of the crystallinities and Jc values of the (Y,Gd)BCO films.

Improvement of the conversion efficiency of as-deposited Bi2S3/PbS solar cells using a CeO2 buffer layer

We evaluated the performance of CeO2 as a buffer layer for emerging thin-film solar cells. Thin films of CeO2 were deposited via spin coating on transparent conductive oxide (TCO) glass substrates. The photovoltaic parameters of open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and conversion efficiency of the reference samples increased from 134 mV, 4.14 mA/cm2, 0.26, and 0.14% to 254 mV, 14.74 mA/cm2, 0.34, and 1.27%, respectively, by using the structure TCO/CeO2/Bi2S3/PbS. The crystallite size of the absorber layer (PbS) increased from 14 to 24 nm using a 130 nm CeO2 buffer layer.

Enhancement of Critical Current Density of Yttrium Barium Copper Oxide Thin Films by Introducing Nano dimensional Cerium Oxide Defects

The critical current density, Jc  has been the most important parameter used in the design and engineering of effective devices which is one of the implementation of high temperature superconductors (HTSC). In this work, an effort has been made to further improve the critical current density of YBa2Cu3O7-x (YBCO) thin films by preventing the magnetic flux line lattice against the Lorentz force by pinning it in place with the aid of nano-dimensional defects. These defects were generated by distributing nano sized CeO2 islands after YBCO layer was created on LaAlO3 substrates perpendicular to the film using pulsed laser deposition (PLD) technique. Three samples with buffer layers of CeO2 were prepared. CeO2 with 50 pulses, 100 pulses and 150 pulses, after each 1000 pulses of YBCO were prepared five layers for each of the samples. The structural characterization of YBCO/CeO2 and YBCO pristine films were carried out using x-ray diffraction (XRD) and scanning electron microscopy (SEM). Superconducting proprieties were measured using a vibrating sample magnetometer (VSM). Jc  for the pure YBCO and the YBCO/CeO2 films were calculated from magnetization (M) versus Field (H) loops using Bean’s model. Jc  for the 50 pulses of YBCO/CeO2 films was found to be increased slightly by an order of magnitude of about 40% with respect to those of YBCO films without the nano dimensional defects.

Preparation of biaxially textured Ce1-x(Y0.2Zr0.8)xOδ buffer layers on RABiTS NiW tapes by chemical solution deposition

Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00 l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor.

Effect of post-annealing in low oxidizing atmosphere on the properties of CeO2 buffer layer for coated conductors

CeO2-x thin films have been fabricated by chemical solution deposition (CSD) technique on bi-axial textured Ni5W substrates. The effect of post-annealing in moderate oxidizing atmosphere on the structure and texture of the film has been studied by varying temperature and CO2 concentration during the post-annealing process. The results show that the structure and texture stability of the CeO2-x film is heavily dependent on the post-annealing temperature. A high post-annealing temperature could lead to the change of cerium valence and even oxidation of Ni5W substrate. In addition, an excess amount of CO2 could cause the degeneration of texture degree and surface flatness of CeO2-x film because of the increase of oxygen vacancy defects and the production of carbonates. Except effective removal of residual carbon in films, therefore, the production of both the oxygen vacancy concentration and carbonates should be greatly controlled to improve the texture degree and surface flatness of CeO2-x films by adjusting the concentration of oxidizing gas and the heat-treatment temperature during the post-annealing process or the YBCO deposition process. Moreover, the CeO2-x film post-annealed at 700 °C in the mixture atmosphere with 1% CO2 show sharper texture and smoother surface because of the existence of small amount of oxygen vacancy and carbonates compared with the as-prepared sample.

Performance of La0.8Sr0.2Ga0.8Mg0.2O3-based SOFCs with atmospheric plasma sprayed La-doped CeO2 buffer layer

Ce0.6La0.4O2 (LDC) is a promising buffer layer for preventing chemical reactions between a doped-LaGaO3 electrolyte and Ni-based anode in intermediate-temperature solid oxide fuel cells (SOFCs). In the present work, first, the chemical compatibility between La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) powders and LDC powders is evaluated. Subsequently, an LDC buffer layer is prepared via atmospheric plasma spraying (APS) at different deposition temperatures using powders that have particle sizes larger than 30 μm. The effects of deposition temperature on the microstructure and ionic conductivity are investigated. Cells with an optimized APS LDC interlayer between the NiO containing anode and LSGM electrolyte are tested with humidified H2 as fuel and ambient air as the oxidation. At 750 °C, the maximum power density of cells with the APS LDC interlayer is 460 mW/cm2. In addition, a stability test of ∼400 h at 650 °C under a constant current density of 250 mW/cm2 is carried out, and the cell with the optimized APS LDC interlayer is stable. Therefore, APS is a viable alternative approach for fabricating an LDC interlayer for SOFCs using the LSGM electrolyte.

Trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films on CeO2 buffered R-plane Al2O3 substrates

(Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films were grown on CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). Annealing of the CeO2 buffered R-Al2O3 substrates was performed to control the crystallinity and surface morphology of the CeO2 buffer layer. The annealing treatment led to a significant improvement in the crystallinity and surface morphology of the CeO2 buffer layer. A (Y,Gd)BCO film grown on the CeO2 buffer layer with high crystallinity and an atomically flat surface exhibited high self-field (at 77 K) and in-field (at 20 K, 9 T, μ0H∥c) critical current densities (Jc). Annealing of the CeO2 buffer layer thus enabled enhancement of not only the self-field Jc for the (Y,Gd)BCO film but also the in-field Jc.

Uncovering a new quasi-2D CuO2 plane between the YBa2Cu3O7 and CeO2 buffer layer of coated conductors

We report a discovery of the quasi-two-dimensional (quasi-2D) CuO2 plane between the superconductor YBa2Cu3O7 (YBCO) and CeO2 buffer layer (mostly used in the fabrication) of coated conductors through the atomistic computer simulations with the molecular dynamics (MD) and first-principle calculations. For an YBCO coated conductor with multilayer structures, the buffer layers deposited onto a substrate are mainly considered to transfer a strong biaxial texture from the substrate to the YBCO layer. To deeply understand the tuning mechanism of the texture transfer, exploring the complete atomic-level picture of the structure between the YBa2Cu3O7/CeO2 interfaces is firstly required. However, the related observation data have not been available due to some big challenges of experimental techniques. With the MD simulations, having tested the accuracy of the potential functions for the YBa2Cu3O7/CeO2 interface, we constructed a total of 54 possible atom stacking models of the interface and identified its most appropriate and stable structure according to the criterion of the interface adhesion energy and the coherent characterization. To further verify the stability of the identified structure, we performed the first-principle calculations to obtain the adhesion energy and developed the general knowledge of the interface structure. Finally, a coherent interface formed with a new built quasi-2D CuO2 plane that is structurally similar to the CuO2 plane inside bulk YBCO was determined.

Epitaxial Growth of CeO2 Buffer Layers on IBAD-Textured MgO Templates by Pulsed Laser Deposition

Epitaxial Growth of CeO2 Buffer Layers on IBAD-Textured MgO Templates by Pulsed Laser Deposition

Optimization of BaHfO3 Doping Concentration as Secondary Phase in Y0.5Gd0.5Ba2Cu3O7−x Thin Film Prepared by Pulsed Laser Deposition

BaHfO3 (BHO)-doped Y0.5Gd0.5Ba2Cu3O7−x (YGBCO) films with a series of doping concentrations (1, 3, 5, and 10 mol%) were fabricated on CeO2 buffer layers by pulsed laser deposition (PLD) technique, and a pristine YGBCO film was also deposited at the same conditions for comparison. X-ray diffraction (XRD) results showed that the undoped and doped YGBCO films had a pure c-axis orientation. While the surface morphology and crystal quality of the BHO-doped YGBCO films deteriorated as the BHO content increased, and the critical current density (J c) at 77 K and self-field ( $J_{\mathrm {c}}^{77,0})$ and critical transition temperature (T c) of the BHO-doped YGBCO films exhibited varying degrees of decline in comparison with the pristine YGBCO film. However, the 5 mol% BHO-doped YGBCO film exhibited greatly enhanced the J c and the highest pinning force densities (F p) at both 4.2 and 65 K, which showed the maximum value of 5776 GN/m3 (4.2 K, H//c) and 117 GN/m3 (65 K, H//c), about 1.5 times that of the undoped YGBCO film. Based on the results, the 5 mol% BHO-doped YGBCO film had the most effective flux pinning centers, which are responsible for strongly improved critical current densities in magnetic fields.

Stabilizing new bismuth compounds in thin film form

Abstract