Zr-doped Samples Research Articles

The structure, defects, electrical and magnetic properties of BiFe1−x Zr x O3 multiferroic ceramics

BiFe1−x Zr x O3 (x = 0.00–0.30) ceramics were synthesized using solid state reaction method followed by rapid liquid phase sintering, and the microstructure, electrical and magnetic properties of the synthesized ceramics were systematically investigated. The XRD patterns show that no impurity phases exist in Zr doped samples; Zr doping induces the crystal structure distortion when x ≤ 0.10, and a structural phase transition occurs when the content of Zr varies from 0.10 to 0.20. SEM observations indicate that the average grain size is remarkably decreased by Zr doping. Positron annihilation lifetime spectra results indicate that cation vacancy-type defects exist in all samples, the cation vacancy concentration increases with increasing Zr content from 0.00 to 0.20, and then decreases with further increase of Zr content. Electrical and magnetic measurements show that enhanced leakage, ferroelectric and magnetic properties are observed in Zr doped ceramics. The analysis of microstructure and properties show that the cation vacancy defect plays an important role in modulating the electrical and magnetic properties of BiFeO3.

Improving bulk Ca3Co4O9 thermoelectric materials through Zr doping

ABSTRACTCa3Co4−xZrxOy polycrystalline ceramics with small Zr substitution have been prepared through the classical solid-state method. X-ray diffraction data have shown that all samples are composed only of Ca3Co4O9 and Ca3Co2O6 phases. Moreover, by increasing Zr substitution up to 0.07, Ca3Co2O6 phase content is decreased. Density measurements have revealed that all samples are very similar, with values around 74% of the theoretical density. Electrical resistivity is decreased in Zr-doped samples, with respect to the pure samples, while Seebeck coefficient is unchanged. Both factors lead to power factor values around 0.33 mW K−2 m−1 at 800°C in 0.07 Zr-doped samples, which are about 65% higher than those obtained for the undoped samples.

Local environments and transport properties of heavily doped strontium barium niobates Sr0.5Ba0.5Nb2O6

Undoped as well as K-doped (40%), Y-doped (40%), Zr-doped (10%), and Mo-doped (12.5%) strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN50) materials have been investigated to explore the effect of heavy doping on the structural and functional properties (thermo-power, thermal and electrical conductivities) both in the as prepared (oxidized) and reduced states.For all materials, the EXAFS spectra at the Nb – K edge can be consistently analyzed with the same model of six shells around the Nb sites. Doping mostly gives a simple size effect on the structural parameters, but doping on the Nb sites weakens the Nb–O bond regardless of dopant size and charge. Shell sizes and Debye–Waller factors are almost unaffected by temperature and oxidation state, and the disorder is of static nature.The functional effects of heavy doping do not agree with a simple model of hole or electron injection by aliovalent substitutions on a large band gap semiconductor.With respect to the undoped samples, doping with Mo depresses the thermal conductivity by ~ 30%, Y doping enhances the electrical conductivity by an order of magnitude, while Zr doping increases the Seebeck coefficient by a factor of 2–3. Globally, the ZT efficiency factor of the K-, Y-, and Zr-doped samples is enhanced at least by one order of magnitude with respect to the undoped or Mo-doped materials.

Ceria and Ce0.95M0.05O2 − δ mixed oxides (M = La, Pr, Zr): Vacancies and reducibility study

Highly reducible and redox active mixed oxides are employed in selective oxidation reactions and fuel cells, among others. Ceria is a renowned material in these applications because of its capacity to take and release oxygen. At the same time, these properties may be enhanced by cerium substitution with certain elements, usually, other rare earths. In this line, the present work is focused on the preparation of pure cerium oxide and doped with 5%at of La, Pr or Zr. The solids were calcined at 600, 750 and 900°C and characterized by diverse techniques (DRX, BET, Raman, OSC-OSCC, H2-TPR).When increasing calcination temperature, it was observed an improved specific surface and crystallite diameter conservation for La and Zr-doped samples. Oxygen vacancy generated by doping, observed both by Raman and OSC-OSCC, decreased with higher calcination temperatures for every solid. Ce0.95Pr0.05O2−δ showed a maximum oxygen storage capacity for 750°C calcination temperature consistent with Raman spectroscopy and hydrogen reduction profiles.

Effects of Zr substitution on structural, morphological, and magnetic properties of bismuth iron oxide phases

The present study involves co-precipitation method to grow un-doped and Zr-doped bismuth iron oxide with . The molar solutions of ferric chloride (FeCl3), zirconyle chloride (ZrOCl2), and bismuth chloride (BiCl3) are prepared in distilled water, and are allowed to react with sodium hydroxide (NaOH). The synthesized powders are then converted into pellets, which are sintered at 500 °C for two hours in a muffle furnace. X-ray diffraction (XRD) shows multi-phase formation in un-doped and Zr doped samples. Scanning electron microscope (SEM) depicts layered structure at low Zr concentration , while uniform surface with smaller grains and voids is observed at , but at , cracks and voids become prominent. The ferromagnetic nature of the un-doped sample is observed by vibrating sample magnetometer (VSM), while paramagnetic behavior appears due to Zr doping. The ferromagnetism in un-doped sample is lost by Zr doping, which is due to the formation of additional Fe–O–Zr bonds that induce paramagnetic behavior.

Study of the physical properties of amorphous Zr doped Al2O3 powders

Alumina (Al2O3) powders doped with different amounts of zirconium (Zr) ions were synthesized by the sol-gel process. The Zr concentration was changed from 0 to 3%. Here we attempted to fabricate Zr doped Al2O3 samples and characterized them for their optical and structural properties. Ultraviolet-Visible analysis (UV-Vis), infrared spectroscopy (FT-IR) and powder X-ray diffraction (XRD) have been used to characterize the optical properties, phase evolution and crystallinity of the obtained samples. X-ray diffraction patterns revealed that all the Al2O3 powders obtained were completely amorphous. An optical study was employed to determine the band gap of the samples. The transmittance had decreased from 90 to 86% and the band gap of pure Al2O3 was found to be 4.116eV, and it was shifted to 4.038eV for 3% Zr doped Al2O3. The results obtained in this study are discussed comparatively with those cited in the literature.

Preparation of Zr-doped CaTiO3 with enhanced charge separation efficiency and photocatalytic activity

A series of Zr-doped CaTiO3 powders were prepared with the mild co-precipitation method and calcined at 850 °C for 3 h. The as-prepared Zr-doped CaTiO3 samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectra (XPS). XRD result revealed the presence of single perovskite phase of CaTiO3. UV–Vis diffusive reflection spectra of Zr-doped CaTiO3 indicated that the absorbance obviously increased in the visible light irradiation. XPS analysis showed that two types of oxygen existed on the photocatalyst surface, including lattice oxygen and absorbed oxygen. Their photocatalytic activity in the case of the degradation of methyl orange in water and photoelectrochemical activity were also tested. The 5%Zr-doped (mole fraction) CaTiO3 sample showed the highest photocatalytic activity. The enhanced photocatalytic activity was ascribed to the change of the lattice structure, existence of oxygen vacancies and increase of the photogenerated charge separation efficiency.

Dielectric Properties of Zr substituted Barium Strontium Titanate

The correlation between the dielectric properties and the structural characteristics of Zr substituted Ba0.6Sr0.4TiO3 (Barium Strontium Titanate) ceramics were investigated under different sintering conditions in this work. (Ba0.60Sr0.40ZryTi1−yO3) (y=0.1, 0.15 and 0.2) nanosized powders is synthesized by conventional solid state reaction method. The formation of (Ba0.60Sr0.40ZryTi1−yO3) was confirmed by XRD. The X-ray analysis reveals that all synthesized Ba0.60Sr0.40ZryTi1−yO3powders have a cubic perovskite structure. The influence of Zr content doping on the grain size and dielectric properties of BST, including dielectric constant and loss tangent were investigated. FE- SEM images show that, the average particle size is reduced with increasing Zr content and the average grain size is in the range 100–200 nm and the well dispersed nano powders have narrow grain size distribution. Dielectric characteristics were measured using Impedance Analyser over a range of frequencies (1kHz to 1MHz). The results show that, the dielectric constant has enhanced with doping of Zr whereas the loss tangent decreases. The particular composition is an excellent candidate for supercapacitor applications. The reduction in loss for Zr doped samples may be due to reduction in vacancy concentration and fine grain size of BST ceramic resulting in its excellent dielectric properties.

The Improvement of Discharge Capacity of Zr-doped Lithium Titanate for Lithium Ion Batteries

Li 4 Ti 5−x Zr x O 12 (0 ≪ x ≪ 0.05) materials are synthesized via one-step liquid method in this work. The morphology, elemental distribution and lithium storage performance of Zr-doped lithium titanate are systematic analyzed by field emitting scanning electron microscopy (FE-SEM, Hitachi S-4800), energy dispersive X-ray (EDS) and Land battery test system (LAND CT2001A) together with the pristine lithium titanate for comparison. The FE-SEM images show the uniform morphology and narrow particle size distribution of Zr-doped samples. The cycle performance measurements demonstrate that the Li 4 Ti 4.97 Zr 0.03 O 12 electrode displays the best discharge capacities among the composites. It delivers the initial discharge capacities of 165.4 mAh/g and 152.9 mAh/g at 5C and 10C, and remains the values of 142.9 mAh/g and 127.4 mAh/g after 200 cycles. Furthermore, the charge and discharge curves exhibit that the Zr-doped composite presents smaller polarization than the pristine lithium titanate.

Study on magnetic properties of Ce17Fe78−xZrxB6 (x=0–2.0) alloys

In order to improve the magnetic performances of Ce2Fe14B-type alloys, Ce17Fe78−xZrxB6 (x=0–2.0) were synthesized by a melt spinning method at a quench wheel velocity of 35m/s. The crystal structure and hard magnetic properties of Ce17Fe78−xZrxB6 (x=0–2.0) alloys were investigated. The glass forming ability and thermal stability of as-spun ribbons were improved by Zr addition. Zr-doped samples had lower Curie temperature for Ce2Fe14B, implying that Zr atoms could substitute directly into Ce2Fe14B phase. Refinement of X-ray diffraction data showed that the lattice constants and volume fraction of Ce2Fe14B phase for Ce17Fe78−xZrxB6 (x=0–2.0) alloys annealed at optimum temperatures decreased gradually with increasing Zr content. Moreover, the mean grain size of the Ce2Fe14B phase decreased gradually with Zr at% increasing from 0 to 2.0. The analysis of Henkel plots verified that proper Zr content improved the microstructure and enhanced the exchange coupling interaction. When x=0.5, the optimum magnetic properties were obtained: iHc=429.9kA/m, Br=0.48T and (BH)max=4.5MGOe.

Irradiation Response of Next Generation High Temperature Superconductors for Fusion Energy Applications

The latest generations of rare-earth substituted and nano-doped YBa2Cu3O7-x (YBCO) high temperature superconductors (HTS) developed for applications in magnetic fields are being evaluated for potential use in fusion energy applications. The benefits include increased plasma performance and reduced system cost through more compact and cryoplant-free fusion energy systems. The response to ion irradiation of commercially produced GdBa2Cu3O7-x, (Y,Dy)Ba2Cu3O7-x, and Zr-doped (Y,Gd)Ba2Cu3O7-x samples was investigated. These state-of-the-art conductors represent different design methods for enhanced flux pinning, resulting in different responses to radiation damage. Irradiations using 5-MeV Ni and 25-MeV Au ions were used to examine cascade damage while keeping electronic energy loss levels below columnar defect thresholds. An improved radiation tolerance is found in these new generation HTS conductors. Specifically, the influences of irradiation on the superconducting critical temperatures and the electrical transport properties of the samples were much less than that observed on the earlier generation of irradiated HTS materials investigated by others.

Sol–gel combustion synthesis of Zr-doped BaTiO3 nanopowders and ceramics: Dielectric and ferroelectric studies

The dielectric and ferroelectric properties of the ceramic system, Ba(Ti1−x,Zrx)O3, were investigated for compositions 0≤x≤0.2. The primary nanopowders were synthesized using a sol–gel combustion route to obtain the homogenous compounds. X-ray diffraction patterns demonstrated that there was a cubic structure for the prepared nanopowders. The nanopowders were pressed into pellet form and sintered at 1250, 1300, and 1350°C. The results revealed a significant increase in the permittivity of the Zr-doped samples. The sample showed the best dielectric properties and a ferroelectric behavior for the value of x=0.05.

Synthesis, Characterization, and Thermochemical Redox Performance of Hf4+, Zr4+, and Sc3+ Doped Ceria for Splitting CO2

We present results on the thermochemical redox performance and analytical characterization of Hf4+, Zr4+, and Sc3+ doped ceria solutions synthesized via a sol–gel technique, all of which have recently been shown to be promising for splitting CO2. Dopant concentrations ranging from 5 to 15 mol % have been investigated and thermally cycled at reduction temperatures of 1773 K and oxidation temperatures ranging from 873 to 1073 K by thermogravimetry. The degree of reduction of Hf and Zr doped materials is substantially higher than those of pure ceria and Sc doped ceria and increases with dopant concentration. Overall, 10 mol % Hf doped ceria results in the largest CO yields per mole of oxide (∼0.5 mass % versus 0.35 mass % for pure ceria) based on measured mass changes during oxidation. However, these yields were largely influenced by their rate of reoxidation, not necessarily thermodynamic limitations, as equilibrium was not achieved for either Hf or Zr doped samples after 45 min exposure to CO2 at all oxidation temperatures. Additionally, sample preparation and grain size strongly affected the oxidation rates and subsequent yields, resulting in slightly decreasing yields as the samples were cycled up to 10 times. X-ray diffraction, Raman, FT-IR, and UV/vis spectroscopy in combination with SEM-EDX have been applied to characterize the elemental, crystalline, and morphological attributes before and after redox reactions.

Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

Characterization and Optimized Electrochemical Performances of LiFe<SUB>1–2<I>x</I></SUB>Zr<SUB><I>x</I></SUB>PO<SUB>4</SUB>/C Nanocomposites as Cathode Materials for Lithium-Ion Batteries

A series of nanocomposite LiFe(1-2x)ZrxPO4/C (x = 0.01,0.02, 0.03, 0.04, 0.06) were prepared by carbon thermal reduction method. With this strategy, the Li3PO4 impurity phase can be obviously reduced in the Zr-doped samples and the electrochemical performance is obviously improved by Zr doping compared with the undoped one. The best electrochemical performances were observed in LiFe(0.92)Zr(0.04)PO4/C as well as good cycle stability.

Effect of Zr Addition on the Magnetization Reversal Behavior for α-Fe/Pr2Fe14B Nanocomposite Alloys

The microstructure and magnetic properties of the Zr-doped α-Fe/Pr2Fe14B nanocomposite magnets prepared by melt-spinning method have been studied by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The magnetization reversal behavior during the recoil processes of nanocomposite alloys has been investigated by analyzing the hysteresis curves and recoil loops of demagnetization curves. An enhanced magnetic properties has been obtained by the addition of 1 at. % Zr in α-Fe/Pr2Fe14B alloys, where the coercivity Hc increases from 470.7 to 793.2 kA/m, the maximum energy product (BH)max from 66.8 to 90.8 kJ/m3, the remanence ratio Mr/Ms from 0.74 to 0.77. The recoil loop results show that the maximum value of the integrated recoil loop area for 1 at. % Zr doped sample is quietly low of 1.87×10-3, only 1/2 for the Zr-free and 1/3 for 5 at. % Zr doped samples respectively. This result indicates that the 1 at. % Zr doped sample has a lower energy loss, resulting from a low recoverable portion of the magnetization remaining as long as the applied reversal field is below the coercivity Hc. This study provides a promising guideline for the future fabrication of low-energy-loss nanocomposite magnets for electric machines and generators.

Improvement of electrochemical properties of layered LiNi 1/3Co 1/3Mn 1/3O 2 positive electrode material by zirconium doping

To improve the electrochemical properties of LiNi 1/3Co 1/3Mn 1/3O 2, powders of Zr-doped mixed transition metal oxides, LiNi 1/3Co 1/3Mn 1/3-xZr xO 2 (x = 0, 0.01, 0.025, 0.05) (LNCMZ), are synthesized via a thermal polymerization method. Their structure and electrochemical properties are investigated by X-ray diffraction, galvanostatic charge–discharge of LNCMZ/Li half cells, galvanostatic intermittent titration technique (GITT), direct current resistance measurement and AC impedance spectroscopy. All of the prepared LNCMZ samples have a hexagonal α-NaFeO 2 structure whose lattice parameters increase monotonously with the Zr content. The Zr doping results in higher lithium diffusion coefficient in LNCMZ and more stable resistance during the electrochemical cycling of LNCMZ/Li cells so that the Zr-doped samples show notable improvement of cycling performance and rate capability. The sample LiNi 1/3Co 1/3Mn 1/3-0.01Zr 0.01O 2 exhibits the best electrochemical performance with capacity retention of 92.7% during 100 cycles and a capacity of 133.9 mAh g −1 at 8 C rate, corresponding to 71.5% of its capacity at 0.1 C.

Study on Coercivity Mechanism of the Sintered NdFeB Magnets by Zr Addition

The effects of Zr addition on the microstructure and magnetic properties of the sintered NdFeB magnets were investigated by X-ray diffraction (XRD) and BH magnetic tester. The XRD analysis showed that both the Zr-free and Zr-doped samples are composed of main amount of Tetragonal phase Nd2Fe14B (P42/mnm) and trace amount of Nd-rich phase, but adding Zr reduces significantly the values of pole density factor of (004), (006) and (008) crystal faces for the sintered Nd(Fe,Zr)B magnets estimated by Horta-formula. Accordingly, the coercivity of the sample with Zr addition is reduced from 2038 kA/m down to 1951 kA/m. The study of the Kronmüller-plot shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of αk and Neff are obtained also.

EXAFS and Raman scattering studies of Y and Zr doped nano-crystalline tin oxide

Nanocrystals of Y and Zr doped SnO2 have been prepared by sol-gel route and annealed at 200, 400, 600, 800 and 1000 ºC. The X-ray diffraction (XRD) results showed the average size of the particles in the freshly prepared samples to be ~ 3 nm. The Extended Absorption Fine Structure (EXAFS) technique was used to study the dopant environments in nanocrystalline tin oxide. In all Y-doped samples, except the one annealed at 1000 ºC, there is clear evidence that Y has not entered the SnO2 lattice. This is clearly supported by the Raman scattering results. In all Zr-doped samples, there is a simple substitution for Sn by Zr.