Zr-doped Samples Research Articles

Sintering, microstructure, and mechanical properties of ZrO2-doped Al2O3

ABSTRACT In the present work, the effect of Zr-doping on the sintering, microstructure development, and mechanical properties of polycrystalline Al2O3 was studied. Dopant concentrations of 830 and 2070ppm cationic ratio of Zr in Al2O3 corresponding to 2000 and 5000 wt. ppm of ZrO2 in Al2O3, respectively, were used. The sintering schedule of undoped as well as Zr-doped Al2O3 samples was optimised following a series of precoarsening experiments. The Zr-doped Al2O3 ceramics exhibited controlled grain size and improved density. Upon increasing the Zr-dopant concentration from 830 cat. ppm to 2070 cat. ppm. Zr-doped Al2O3 ceramics having a refined microstructure with a homogeneous distribution of controllably grown ZrO2 in Al2O3 matrix was obtained. Microhardness of the Zr-doped samples showed negligible dependence with Zr-doping, whereas mechanical strength was found to improve with it. The improvement in strength was attributed to the combined effect of improved sinter density, microstructural refinement, and grain-boundary strengthening.

The Effect of Doping Process Route on LiNiO2 Cathode Material Properties

The pursuit of higher energy density in lithium-ion batteries has driven the increase of the nickel content in lithium nickel cobalt manganese oxide cathode active materials (CAMs), ultimately approaching LiNiO2 (LNO). The downside of the high specific capacity of LNO is more severe degradation of the CAM during battery operation. A common approach to increase structural stability is the introduction of dopants. Various dopants are discussed and compared with each other when integrated into the CAM and tested against undoped materials in the literature, but little attention is given to the role of the process route of their introduction. In this work, we demonstrate with a series of nominally equally Zr-doped LNO samples that effects on various physico- and electrochemical properties are due not to the dopant itself, as one would assume in comparison to an undoped sample, but to the process route and the resulting particle morphology. Dopant, concentration and process routes (co-precipitation, impregnation and co-calcination) were chosen based on their significance for industrial application.

Low-Lattice Thermal Conductivity in Zr-Doped Ti2NiCoSnSb Thermoelectric Double Half-Heusler Alloys

The effect of doping on the thermoelectric properties of Half-Heusler (HH) high-entropy alloy (HEA) Ti2NiCoSnSb was studied. Lower thermal conductivity was observed with increased Sb doping. Mass scattering by heavy (Ta, Zr) and light (Al) dopants was studied to further lower the thermal conductivity. Dopants at the level of up to 50% at the Ti site were studied. A high HH phase content was obtained in the Zr-doped samples, and a low-lattice thermal conductivity of 1.9 W/(m·K) was observed. This value is one of the lowest reported lattice thermal conductivities in HH alloys. The poor solubility of Ta led to undissolved Ta in the samples, which enhanced the electrical properties. In the case of Al doping, the NiAl phase raised the power factor value of Ti1.8Al0.2NiCoSn0.5Sb1.5 to 2.2 × 10–3 W/(m·K2), which is almost twice the corresponding value reported for Ti2NiCoSnSb. Interestingly, a maximum ZT of 0.29 was found in all of the doped systems, although the transport mechanism and microstructure varied widely with the type of dopant. An optimum dopant level of 25% of Zr, 7.5% of Ta, and 10% of Al is necessary to obtain the maximum ZT in these alloys. Compared to HH systems, the HH high-entropy alloy (HEA) systems provide a larger composition field for tuning the transport properties by simultaneous doping of multiple elements to lower the thermal conductivity.

Exploring a surrogate of Pellet–Cladding interaction: Characterization and oxidation behavior

The present work analyzes the effect of different Zr contents on the microstructure and thermal behavior of non-irradiated UO2. A set of Zr-doped UO2 (0, 20, 40, 80, and 100 wt%) pellets was prepared via solid-state synthesis by mimicking the chemical bonding between ZrO2 and UO2. After sintering, the Zr-doped UO2 monoliths were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Oxidation of the Zr-doped UO2 samples has been monitored by thermogravimetric analysis. Results of thermal behavior under air and low oxygen partial pressure show a profound effect of delayed oxidation with the addition of Zr to UO2 and then an increased oxidation resistance of UO2 to U3O8 when compared to pure UO2 pellet.Graphical abstract

Screening of optimal dopants on cobalt-based ceramics for high-temperature thermochemical energy storage

To date, numerous dopants have been investigated to promote the initial heat storage performance or sintering resistance of Co3O4 for thermochemical energy storage. Owing to the different synthesis methods and heat storage test conditions, the performances of these materials are not comparable. In this work, nine dopants, including four unreported dopants, were systematically compared and screened under the same conditions. Results demonstrated that for five redox cycles, the Si- and Mg- doped sample had adverse effects on the conversion rate, and the others maintained the conversion rate above 0.95. Cu and Zr doping exhibited the highest re-oxidation rate values, and those of the others were lower than that of pure cobalt oxide. Moreover, except for Cu and Zr, all dopants adversely affected energy density. According to aforementioned heat storage properties, Cu-, Zr-doped samples, and pure cobalt oxide were subjected to 100 cycles for further comparison. The Cu-doped sample exhibited a higher re-oxidation rate and energy density, and the Zr-doped sample exhibited more stable cyclability. Finally, by doping Cu and Zr, the micromorphology evolution was more stable than that of pure oxide for multiple cycles, and X-ray photoelectron spectroscopy results revealed that the higher surface oxygen was the primary reason for the superior performance facilitated by Cu and Zr. The Cu- and Zr-modified cobalt oxides were the potential candidates for thermochemical energy storage.

The effect of Zr (IV) doping on TiO2 thin film structure and optical characteristics

Dense thin films of TiO2 and TiO2 doped with Zr4+ were spin coated on glass substrate and annealed at 450 °C. The optical characteristics and crystalline structure were studied using UV–vis, PL, XRD, and SEM. X-ray investigation proved that an anatase phase was formed in all Zr-doped samples (0, 0.5, 1, 5, and 10 %). Zr-doping changes the band gap energy from Eg = 3.48 eV (undoped) to 3.57 eV (1 % doping), along with the large size of Zr4+ results in slight lattice enlargement. Increasing Zr-doping beyond 1.0 % is associated with decreasing the band gap due to amorphization of TiO2. The anatase crystallites growth is stalled with increasing doping; from 23.5 nm to 10.43 nm and micro-strain increases with increasing doping concentration. The changes in optical properties, crystal growth and structure properties are due to lattice strain created by the collective effect of Zr-doping and reduction in crystallite size. Zr-doped TiO2 nanoparticles exhibited typical photoluminescence (PL) matching to the visible spectrum region when excited at 275 nm. The produced thin films had a lower rate of electron–hole recombination than TiO2 that was not doped.

Strategy of Extra Zr Doping on the Enhancement of Thermoelectric Performance for TiZrxNiSn Synthesized by a Modified Solid-State Reaction.

Half-Heusler alloys, which possess the advantages of high thermal stability, a large power factor, and good mechanical property, have been attracting increasing interest in mid-temperature thermoelectric applications. In this work, extra Zr-doped TiZrxNiSn samples were successfully prepared by a modified solid-state reaction followed by spark plasma sintering. It demonstrates that extra Zr doping could not only improve the power factor on account of an increase in the Seebeck coefficient but also suppress the lattice thermal conductivity originated from the strengthened phonon scattering by the superlattice nanodomains and the secondary nanoparticles. As a consequence, an increased power factor of 3.29 mW m-1 K-2 and a decreased lattice thermal conductivity of 1.74 W m-1 K-1 are achieved in TiZr0.015NiSn, leading to a peak ZT as high as 0.88 at 773 K and an average ZT value up to 0.62 in the temperature range of 373-773 K. This work gives guidance for optimizing the thermoelectric performance of TiNiSn-based alloys by modulating the microstructures on the secondary nanophases and superlattice nanodomains.

Dual-Element-Modified Single-Crystal LiNi0.6Co0.2Mn0.2O2 as a Highly Stable Cathode for Lithium-Ion Batteries.

Single-crystalline LiNi0.6Co0.2Mn0.2O2 cathodes have received great attention due to their high discharge capacity and better electrochemical performance. However, the single-crystal materials are suffering from severe lattice distortion and electrode/electrolyte interface side reactions when cycling at high voltage. Herein, a unique single-crystal LiNi0.6Co0.2Mn0.2O2 with Al and Zr doping in the bulk and a self-formed coating layer of Li2ZrO3 in the surface has been constructed by a facile strategy. The optimized cathode material exhibits excellent structural stability and cycling performance at room/elevated temperatures after long-term cycling. Specifically, even after 100 cycles (1C, 3.0-4.4 V) at 50 °C, the capacity retention for the Al and Zr co-doped sample reaches 92.1%, which is much higher than those of the single Al-doped (85.4%), single Zr-doped (87.1%), and bare samples (76.3%). The characterization results and first-principles calculations reveal that the excellent electrochemical properties are attributed to the stable structure and interface, in which the Al and Zr co-doping hinders cation mixing and suppresses detrimental phase transformations to reduce internal stress and mitigate microcracks, and the coating layer of Li2ZrO3 can protect the surface and suppress interfacial parasitic reactions. Overall, this work provides important insights into how to simultaneously build a stable bulk structure and interface for the single-crystal NCM cathode via a facile preparation process.

SmFe12-based hard magnetic alloys prepared by reduction-diffusion process

High phase-purity Sm(Fe0.8Co0.2)11Ti and Sm0.8Zr0.2(Fe0.8Co0.2)11Ti powders with the tetragonal ThMn12 crystal structure have been synthesized by reduction-diffusion method. The average particle size is 1.47 ± 0.82 μm for the Zr-free and 2.29 ± 1.22 μm for the Zr-doped samples. The larger particles are multi-grain, without a chemically distinct grain boundary phase as revealed by TEM investigations. The intrinsic magnetic properties are μ0Ms= 1.42 ± 0.04 T, μ0Ha= 9.8 ± 0.4 T for Zr-free and μ0Ms= 1.37 ± 0.04 T, μ0Ha= 9.7 ± 0.4 T for Zr-doped samples. Temperature-dependent XRD studies show that the ThMn12-type phase begins to decompose around 500 °C which presents difficulties for further development into fully dense bulk magnets. Successful introduction of grain boundary phase with good wettability has been realized by infiltrating low-melting eutectic alloys, resulting in fully dense bulk samples. However, coercivity remains low, μ0Hc = 0.34 T. The underlying microstructural reasons for not achieving large Hc are discussed.

Effect of zirconium doping on the structural, optical, electrochemical and antibacterial properties of ZnO nanoparticles prepared by sol-gel method

Abstract The sol-gel approach has been used to synthesize Zn1-xZrxO (x = 0.00, 0.01, 0.03 and 0.05) nanoparticles. Effect of Zr-doping on structural, optical, electrochemical, and antibacterial properties of ZnO nanoparticles is investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), UV-Visible spectroscopy (UV–Vis), and Photoluminescence (PL) analysis were used for the characterization of undoped and Zr-doped ZnO nanoparticles. Shifting of the absorption edge to lower wavelength and red-shift of the band gap are observed in UV–visible spectra of Zr-doped ZnO samples. Room temperature PL spectra exhibited band edge, violet, strong blue and green emission regardless of the concentration of doping, but intensity increased with levels of doping. Electrochemical performances towards uric acid individually and simultaneously were significantly affected by dopant and superior outcomes were acquired with the Zr-doped ZnO modified carbon paste electrode (MCPE). Antibacterial studies reveal that the Zr-doped ZnO nanoparticles possess improved antibacterial activity against both gram-positive (Bacillus subtilis) and the gram-negative (Klebsiella pneumonia) bacterial strains than the pure ZnO nanoparticles.

Promoting the performances of NaTi2(PO4)3 electrode for sodium ion battery by reasonable crystal design and surface modification

Sodium-ion battery as an attractive energy storage system is acknowledged as alternative to lithium-ion battery on account of their extensive resources and low price. NaTi2(PO4)3 is considered as an excellent electrode material in sodium-ion battery due to open three-dimensional crystal channels for ion diffusion. In this work, reasonable crystal design of Zr doping and surface modification of carbon coating strategy was employed to promote the sodium storage performances of NaTi2(PO4)3 electrode. A series of NaTi2-xZrx(PO4)3/C (x = 0.05, 0.1, 0.15) composites with core@shell structure were synthesized through an easy sol-gel route, and were applied as electrode for sodium ion battery. The result shows that the crystal type of all samples is relatively pure. However, the dispersion of Zr doped samples are significantly improved compared to the blank sample. Among all the samples, NTP-Zr-0.1 (NaTi1.9Zr0.1(PO4)3/C) demonstrates the best charge/discharge performances. It delivers the discharge capacities of 206.3 mA h g-1 at 40 mA g-1 and 79.2 mA h g-1 at 2000 mA g-1, while those of NTP are 116.2 and 26.9 mA h g-1, severally. Superior electrochemical performance of NTP-Zr-0.1 is probably ascribed to the carbon coating structure, good dispersion, and lattice volume increase, further accelerating the transfer of electron and sodium ion. This study implies that carbon coating and Zr doping are facile and efficient strategy for promoting performances of NaTi2(PO4)3/C composite.

Improved Electrochemical Performance of Na3V2−xZrx(PO4)3/C Through Electronic and Ionic Conductivities Regulation

Electronic and ionic conductivities are two key parameters in determining the electrochemical performance of lithium/sodium ion batteries, and element-doping is an effective way to regulate the conductivity of an active material. In this work, we attempt to modify the electronic and ionic conductivities of Na3V2(PO4)3/C cathode through a proper content of Zr-doping and the two kinds of conductivities are distinguished by an ion-blocking measurement method. All Zr-doped samples display significant increase of the electronic conductivity and the x = 0.1 sample possesses the highest value of the electronic conductivity. The ionic conductivity shows a similar variation trend, but the variation value is far smaller than that of the electronic conductivity. The increase of the electronic conductivity is about one order larger than that of the ionic conductivity as x increases from 0 to 0.1. The enhanced electronic and ionic conductivities can considerably improve the cycling and rate performance of the sodium ion batteries using Na3V2(PO4)3/C cathode, especially the rate performance. The x = 0.1 electrode exhibits a much higher capacity in the whole cycling process after 1000 cycles at 10 C rate and its capacity at 50 C is about 5 times larger than that of the pristine sample.

Influence of B-site doping on structural, optical and dielectric properties of bismuth ferrite

The present work discusses the nature of electrical defects that influence the dielectric response of BiFe1-xZrxO3 nanostructures fabricated by hydrothermal method for x = 0.0, 0.005, 0.01, 0.015, 0.02 and 0.025. X-ray diffraction studies reveal that a higher concentration of Zr4+ ions can lead to the formation of an impure phase like Bi2Fe4O9 which increases the leakage current. Besides, the suppression of E-modes in a 1.5% doped sample confirms the structural distortion in FeO6 octahedra. A decrease in the optical band gap of Zr-doped samples indicates the presence of oxygen vacancies as donor levels within the forbidden gap. The dielectric constant of a 1.5% doped sample is quite higher than pure BiFeO3 sample at a frequency below 1 kHz. However, at higher frequency region (>1 kHz) the difference in dielectric constant between 1.5% Zr doped and a pure sample is quite less. Further, the broadened peak of M“(ω) of the doped sample indicates the non-Debye relaxation of charge carriers with different time constants.

Effects of Zr doping to improve ionic conductivity and lithium-diffusion kinetics of β-LiVOPO4 cathode material

We tried to improve the ionic conductivity, lithium-ion diffusion, and cycle capacity of pure β-LiVOPO4 cathode material by Zr doping. Pure and Zr-doped β-LiVOPO4 cathode material was synthesized by a low-temperature sol–gel process. The physiochemical properties of the synthesized materials were analyzed by various characterization techniques. The Zr doping of the β-LiVOPO4 was confirmed by ex situ XANES analysis. The electrochemical behavior of the synthesized material was studied by various electrochemical analyses. The lithium-diffusion coefficient values of pristine and selected Zr-doped β-LiVOPO4 cathode materials were studied and compared using SSCV, EIS, and PITT at different voltages. The calculated values of the diffusion coefficients obtained from CV and EIS are in the range of 10−14–10−13cm2/s. The PITT measurement gives the values of 10−12–10−11cm2/s. All techniques indicated that x=0.03 Zr-doped samples obtained the improved the lithium diffusion coefficient values.

The effect of Zr substitution on saturation magnetization in (Sm1-xZrx)(Fe0.8Co0.2)12 compound with the ThMn12 structure

Zr is one of the essential elements to stabilize the ThMn12 structure in rare earth (R) transition metal (M) hard magnetic compounds, RM12. In this work, the effects of Zr on the intrinsic hard magnetic properties of (Sm1-x Zrx)(Fe0.8Co0.2)12 compounds are investigated using epitaxially grown thin films. The increase of Zr substitution for Sm from x = 0 to 0.26 for (Sm1-x Zrx)(Fe0.8Co0.2)12 increases saturation magnetization (μ0Ms) from 1.78 T to 1.90 T, the highest value reported for hard magnetic compounds. The largest μ0Ha and Tc for Zr-doped samples were found to be 9.8 T and 671 K for x = 0.18 which is superior to those for Nd2Fe14B. Sm-rich Sm1.30Zr0.27(Fe0.8Co0.2)12, obtained as sub-μm thick films, has remanence, μ0Mr of 1 T, which appears to be useful for near-field applications such as micro-electro-machines and magnetic recording media if microstructure can be optimized to obtain a sufficient coercivity.

Effect of zirconium doping in the microstructure, magnetic and dielectric properties of cobalt ferrite nanoparticles

Zirconium doped cobalt ferrite nanoparticles (Co1-xZrxFe2O4 where x = 0, 0.25, 0.50, 0.75 and 1) have been successfully engineered via co-precipitation method. X-ray diffraction studies reveal single phase cubic spinel structures up to Zr content of 50% with average sizes in the range of 16–26 nm.Particle sizes decrease with Zr doping due to increased strain in the crystal lattice. Fourier Transform Infrared and Raman spectra reveal the formation of mixed spinel ferrite particles. Presence of cobalt, zirconium, iron and oxygen in the prepared nanoparticles were identified by X-ray fluorescence analysis. Morphology of the samples investigated by Transmission Electron Microscopy shows the formation of nearly spherical particles. The surface characteristics identified by X-ray photoelectron spectroscopy confirms the substitution of zirconium ions mainly into octahedral sites with partially inversespinel structure. Thermal stability studies proves that ferrite formation to be a continuous process. Electrical properties such as dc resistivity as a function of temperature and ac conductivity with frequency were studied for all samples. The variation of dielectric properties like dielectric constant and dielectric loss are also studied as a function of frequency and these results reveal that the dispersion is due to interfacial polarization and hopping of charge carriers. Saturation magnetization, remanence and coercivity values changes with Zr substitution. The high coercive field obtained for Zr doped samples reveals their ferromagnetic nature suggesting a wide range of applications in telecommunication, data processing, consumer electronics, aerospace, catalysis and bio surgical applications.

Scintillation properties of Ti- and Zr-doped lanthanum hafnate single crystals

Undoped, Zr-doped and Ti-doped La2Hf2O7 single crystals were grown by the optical floating zone technique to evaluate the scintillation properties. The synthesized single crystals show scintillation signals with a broad peak around 450 nm. The scintillation decay curves indicate the decay time constants are in nanoseconds order. Suggested from the pulse height spectra under 241Am alpha-ray irradiation, the scintillation light yields of the undoped, Zr-doped and Ti-doped crystal samples are 270, 180 and 390 photons/MeV. From these results, Ti-doping seems to enhance the scintillation properties of a La2Hf2O7 crystal.

Effect of structure distortion and oxygen vacancy on ferromagnetism in hydrothermally synthesized CeO2 with isovalent Zr4+ doping

The influences of isovalent Zr4+ doping on structure and ferromagnetic property in hydrothermally prepared nanoscale CeO2 are investigated. Results suggest that Zr ions tend to incorporate into substitutional sites and then occupy interstitial sites or the surface at a critical doping concentration. The substituted incorporation of Zr4+ can significantly increase structure distortion and facilitate reduction of Ce4+ and production of oxygen vacancies (VO). With Zr doping, the saturation magnetization (MS) increases and then decreases, where the maximal MS appears at Ce0.94Zr0.06O2 sample. Air annealing Ce0.94Zr0.06O2 sample leads to the reduction of ferromagnetism. PL analyses reveal the emergent ferromagnetism may be closely related to structure distortion and VO defects induced by Zr on substitutional sites. The VO mediated F-center exchange mechanism can be used to interpret the RT ferromagnetic behavior in Zr-doped samples.

Effects of Zr Doping on Magnetic and Structural Properties of DyBa2Cu3O <inline-formula> <tex-math notation="LaTeX">$_{7-\delta }$</tex-math> </inline-formula> Thin Films

DyBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> -Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> thin films (with x = 0.00, 0.02, 0.04, and 0.06) were synthetized using the chemical solution deposition method on single crystalline LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates. Effects resulting from Zr doping were investigated by means of magnetic and structural measurements. X-ray diffraction analysis demonstrated a strong c-axis orientation in the DyBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> thin films, with only minor reflections due to the presence of Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phases. Narrow transitions with ΔTc ranging from 1 to 2 K for samples with x = 0.00 and 0.06, respectively, were observed in ac magnetic susceptibility curves, where the nondoped sample demonstrated the highest T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">onset</sup> of 91.7 K compared to the Zr-doped samples. Critical current densities J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of the thin films were obtained from magnetization loop measurements with applied magnetic fields up to 6 T and by employing the Bean model. The sampled doped with 4% Zr exhibited the highest J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> value (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 3.5 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , self-field, 77 K) in the low field range and we, in general, observed that Zr-doped films demonstrated higher values compared to the pure sample. Pinning force plots (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> versus B) reveal a significant improvement over the magnetic field range investigated of the maximum pinning force for Zr-doped samples. We found F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Max</sup> = 1.7 GN/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 3.8 GN/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for pure and 6% Zr samples, respectively. Analysis based on the Dew-Hughes model shows that normal surface pinning is the dominating pinning mechanism.

Reactivity of Ni, Cr and Zr doped ceria in CO2 splitting for CO production via two-step thermochemical cycle

This work focuses on modification and screening of ceria-based oxides for solar H2O/CO2 splitting via two-step thermochemical cycle. Ce1-xMxO2-δ (M = Zr, Ni, Cr; x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized via sol-gel method and tested for CO2-splitting via two-step thermochemical cycles. Reduction was conducted at 1500 °C through a ramp rate of 10 °C/min and oxidation was performed at 1000 °C isothermally. Both Ni and Cr showed low solubility in ceria and no or very limited promoting effect on CO productivity. Cr could be reduced in the first reduction step but cannot be oxidized by CO2 in the following oxidation step. Zr doped sample showed advantages in both CO productivity and lattice stability. 15% Zr doped exhibited the best performance with the CO productivity of 315.40 μmol/g. However, the oxidation rate of Zr doped samples was much lower than that of pure ceria. Compromise between fuel productivity and fast kinetics should be made in practical application.