Zr Substitution Research Articles

Impedance spectroscopic studies of zirconium substituted 0.8BaTiO3-0.2Bi0.5K0.5TiO3 lead free ceramics

Zirconium substituted 0.8BaTiO3-0.2Bi0.5K0.5TiO3 lead free ceramic materials were prepared by solid state reaction followed by high energy ball milling process. To understand its frequency dependent electrical properties, impedance spectroscopic studies were carried out. From the impedance studies it is observed that relaxation taken place from 375 °C. Single depressed semicircle was observed from the Cole-Cole plots. This indicates non-Debye kind of relaxation process. Grain resistance value was calculated from the Cole-Cole plots and it is found to be increasing with increase of Zr substitution. Modulus spectroscopic studies also confirm the non-Debye kind of relaxation process in the material. Variations in normalized values of / max & / max as a function of logarithm of frequency indicates short range conductivity in the present material.

Effect of Preparation Method and Ni2+ Substitution on the Structural, Thermal, and Optical Properties of Nanocrystalline Lanthanum Zirconate Pyrochlore

In order to establish the effective application of materials in a particular area, it is important to first investigate the physical and chemical properties, such as the crystallinity, structure, and the optical and surface properties. The objective of the present study is to fabricate thermally stable pyrochlore oxides, namely, lanthanum zirconate (La2Zr2O7, LZ) and Ni-doped lanthanum zirconate (La2Zr1.5Ni0.5O7, LZN) by the solid-state and sol-gel methods. The effects of the preparation and substitution of Zr4+ by Ni2+ for the resulting nanocrystalline samples were characterized in terms of structure, purity, porosity, the thermal and optical properties, and photoluminescence by different techniques: XRD, FT-IR, BET, EDS, TG-DTG, UV-Vis-DRS, and PL. The XRD results confirm that the pyrochlores prepared via the sol-gel method (LZ-sg and LZN-sg) had a cubic unit-cell lattice, whereas the solid-state method (LZ-s and LZN-s) had impurities of the oxides. The XRD patterns, LZ-sg and LZN-sg, were further treated with the Rietveld technique. The textural measurements reveal that LZ-sg had a higher BET surface area compared to LZN-sg. In addition, the substitution of Zr4+ by the Ni2+ ion provides rational evidence for the improvement in the oxygen mobility, as well as the optical and photoluminescence properties through the lowering of the optical band energy and the electron–hole pairs.

Enhanced transport properties of Sn‐substituted proton‐conducting BaZr0.8Sc0.2O3–δ ceramic materials

AbstractHigh‐temperature proton conductors based on acceptor‐doped barium zirconate exhibit excellent chemical stability in atmospheres containing CO2 or H2O. However, due to their refractory nature, these conductors have a low grain growth rate, which negatively affects the overall electrical conductivity. A possible strategy for increasing the ionic conductivity of zirconates lies in the partial substitution of Zr‐ions with other isovalent dopants. In this work, we carried out systematic studies of the crystal structure, microstructure, hydration capacity, transport, and thermal properties of BaZr0.8–xSnxSc0.2O3–δ (x = 0, 0.1, and 0.2). According to X‐ray powder diffraction and scanning electron microscopy data, all studied ceramic samples have a cubic perovskite structure, whose average grain size decreases with tin doping. It is found that the composition with x = 0.1 exhibits the highest values in terms of total, ionic, grain, and grain‐boundary conductivities. The complex analysis of the obtained data shows that a low‐level substitution of Zr4+‐ with Sn4+‐ions is a competent approach for designing new proton‐conducting electrolytes attractive for high‐temperature applications.

First-principles calculations to investigate Zr substitution enhanced thermoelectric performance of p-type ZrxHf1−xCoBi (x = 0,0.25,0.5,0.75,1) compounds

Based on the first-principle calculation and semi-classical Boltzmann transport theory, the electronic structures and thermoelectric properties of Hf1−xZrxCoBi (x=0,0.25,0.5,0.75,1) compounds have been systematically investigated. These compounds possess narrow bandgaps and they are thermodynamically stable. The low frequency optical branches couple with the acoustic modes in the Zr doped compounds, which highly enhance the phonon scattering. The Zr substitutions hardly reduce the power factors when x=0.25 and 0.75, but substantially reduce the thermal conductivity and thus, improve the figure of merit. The predicted ZT of p-type Hf0.75Zr0.25CoBi and Hf0.25Zr0.75CoBi can reach up to 2.74 and 2.59 at 1200 K, which is much larger than that of the pure HfCoBi compound. This work implies that Hf0.75Zr0.25CoBi and Hf0.25Zr0.75CoBi are promising high-efficiency thermoelectric materials.

Stability of Zirconium-Substituted Face-Centered Cubic Yttrium Hydride.

The stability of a zirconium (Zr)-substituted face-centered cubic (FCC) yttrium (Y) hydride (Y1-xZrx hydride) phase was investigated experimentally and theoretically. Two possible sites for hydrogen atoms exist in the FCC structure, namely, T- and O-sites, where hydrogen is present at the center of the tetrahedron and the octahedron composed of Y and/or Zr metals. The P-C isotherms revealed that the hydrogen content per metal (H/M) with 33% Zr-substituted YH3-δ was 2.2-2.3, which was lower than the expected value calculated from the starting composition of YH3-33% ZrH2 (Y0.67Zr0.33H2.67, H/M = 2.67). Hydrogen at the O-site in Y1-xZrx hydride mainly reacted during hydrogen desorption/absorption. On the basis of theoretical analyses, the hydrogen atoms do not occupy the center of the octahedron, when at least two of the six vertices of the octahedron were composed of Zr. The O-sites, where more than two Zr atoms coordinate, nonlinearly increased with the Zr content, and when the Zr content was >50%, almost no hydrogen atoms occupy the O-sites. The theoretical discussion supported the experimental results, and the Zr substitution was confirmed to reduce the occupancy of H at the O-site in the FCC YH3 significantly.

Influence of Sn4+ substitution for Zr4+ in Nd2Zr3(MoO4)9 and the impact on the crystal structure and microwave dielectric properties

In this work, Nd2(Zr1-xSnx)3(MoO4)9 (0.02 ≤ x ≤ 0.1) (NZSM) ceramics were successfully obtained through conventional solid-state route. Phase analysis, microstructure, and properties were investigated scientifically by XRD, SEM, and network analyzer, respectively. XRD results revealed that all samples with different substitution amounts of Sn4+ formed the pure phase with R-3c space group. The permittivity was related to the polarizability and the bond of Zr2-O5, the bond of Nd-O2 possessed a positive influence on Q×f. The reduced octahedral distortion and increased bond energy made the temperature coefficient more stable. Infrared reflection spectrum results showed that the permittivity was mainly caused by the absorption of phonon oscillation. The optimum properties (εr = 10.34, Q×f = 74,795 GHz, τf = −13.55 ppm/°C) were obtained when x = 0.02 sintered at 750 °C.

Heterovalent Cation Substitution to Enhance the Ionic Conductivity of Halide Electrolytes.

Application of halide electrolytes including Li3InCl6 in all-solid-state lithium-metal batteries is still challenging due to the instability with lithium metal and limited ionic conductivity compared with liquid electrolytes and some sulfides. Here, through Zr substitution, a novel Li2.9In0.9Zr0.1Cl6 electrolyte is synthesized through the ball milling and subsequent annealing process. The ionic conductivity of Li2.9In0.9Zr0.1Cl6 (1.54 mS cm-1 at 20 °C) is nearly double that of original Li3InCl6 (0.88 mS cm-1 at 20 °C). Such conductivity enhancement is mainly attributed to the enlarged interplanar spacing and lattice volume, improved concentration of lithium-ion vacancies created by introducing higher-valence Zr4+, and the change of the preferred orientation from the (001) plane to the (131) plane. As a result, the all-solid-state lithium-metal batteries (ASSLMBs) assembled with the Li2.9In0.9Zr0.1Cl6 electrolyte also demonstrate a higher charge/discharge capacity, better cycle stability, and rate performance during cycling without an extra lithium source at the anode side.

Improvement of microstructure and fracture toughness of MASC alloy by element substitution of Zr for Hf

To improve microstructure and fracture toughness of MASC alloy, the effects of element substitution of Zr for Hf on the microstructure and room-temperature fracture toughness in Nb-24.7Ti-16Si-xHf-yZr-2.0Cr-1.9Al (x + y = 8.2) alloys have been investigated in this study. The results show that the substitution of Zr for Hf in MASC alloy promotes the eutectic reaction of (Nb, X)3Si phase → Nbss/γ(Nb, X)5Si3 eutectic, and shifts the eutectic point to higher Si content, which leads the microstructure transformation from hypereutectic structure to nearly eutectic structure. The primary γ(Nb, X)5Si3 phase content decreases and Nbss phase content increases with the increase of Zr content. The room-temperature fracture toughness increases with the increase of Zr content, and the room-temperature fracture toughness values of 4Zr-4.2Hf, 6Zr-2.2Hf and 8.2Zr-0Hf alloys are 16.03–16.29 MPa m1/2. The room-temperature fracture toughness value of 16.29 MPa m1/2 is the highest value in the nondirectionally solidified Nb-Si based alloys.

Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of M12+–M24+ Substituted M-Type Sr-Hexaferrites

Mn–Ti, Zn–Ti, Zn–Zr substituted M-type Sr-hexaferrites (SrM), SrFe12−2xM1xM2xO19 (0 ≤ x ≤ 2.0, M1 = Mn or Zn; M2 = Ti or Zr) were synthesized, and their solubility, crystalline structure, and high-frequency properties were studied. Zn–Zr substitution caused a relatively large lattice parameter change and resulted in lower solubility (x ≤ 1.0) in the M-type phase compared with Mn–Ti and Zn–Ti substitutions. However, the ferromagnetic resonance frequency (fFMR) effectively decreased with increasing x in SrFe12−2xZnxZrxO19 (Zn–Zr:SrM) (0 ≤ x ≤ 1.0) and the electromagnetic wave (EM) absorption frequency also varied according to the shift in fFMR in the 7–18 GHz range. This is attributed to a gradual decrease in the magnetocrystalline anisotropy of Zn–Zr:SrM (0 ≤ x ≤ 1.0) with an increase in x. Zn–Zr:SrM (x = 0.9)–epoxy(10 wt%) composites exhibited a high EM absorption in the X-band (8–12 GHz) with the lowest reflection loss of <−45 dB. The sample with x = 0.8 showed a broad Ku band (12–18 GHz) absorption performance satisfying RL <−19 dB at 11 ≤ f ≤ 18 GHz.

Effects of Ti substitution for Zr on the electrochemical characteristics and structure of AB2-type Laves-phase alloys as metal hydride anodes

The structural composition and electrochemical capacity of four AB2 Laves-type intermetallic alloys with various Ti/Zr ratios (TixZr1−xLa0.03Ni1.2Mn0.7V0.12Fe0.12, x = 0.12, 0.15, 0.18, and 0.22) were investigated in this study. The alloys were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. These data revealed the coexistence of the main phase of the C15-type FCC Laves-type AB2 compounds with a secondary La–Ni intermetallic that was present in minor amounts. Increasing the Ti substitution for Zr caused the gradual shrinkage of the unit cells of the C15 phase. The neutron powder diffraction studies demonstrated that in the trihydride (Ti, Zr, V)(Ni, Mn, Fe, V)2D3.2, D atoms filled A2B2 tetrahedra, whereas V atoms occupied not only conventional 16d sites but also partially replaced Zr/Ti at 8a sites. All studied alloys showed similar activation behaviors, wherein four cycles were required to realize the highest electrochemical capacity of the anodes. The Ti12/Zr88 alloy demonstrated excellent full discharge capacity that reached 466 mAh/g. The Ti22/Zr78 alloy electrode exhibited good cycling stability (retention rate of ~71%) after 500 cycles and a superior high-rate discharge capability (retention rate of ~71%) at a discharge current density of 400 mA/g. The cycling of the Ti22/Zr78 alloy electrode was studied by electrochemical impedance spectroscopy (EIS) to understand the reasons for the deterioration of cycling capacity, which was related with the pulverization of the alloys and increase in irreversible capacity.

Influence of (Zn1/3Ta2/3)4+ substitution for Zr4+ in Ce2Zr3(MoO4)9 and the impact on the crystal structure and microwave dielectric properties

Ce2[Zr1−x(Zn1/3Ta2/3)x]3(MoO4)9 compounds were successfully prepared and researched. Phase analysis, microstructures and properties were studied scientifically by XRD, SEM and network analyzer, respectively. Rietveld refinement of all compositions confirmed that a single phase in trigonal crystal structure with R-3c space group was obtained. Infrared reflection spectrum results showed the permittivity was related to the absorption of phonon oscillation. SEM images revealed that the average grain size decreased with the increase of (Zn1/3Ta2/3)4+. Microwave dielectric properties analysis indicated that the permittivity was related to the polarizability, Mo-O made a more significant contribution to the Q × f , and τf was related to the octahedral distortion. The optimum properties (εr = 10.77, Q × f = 74,682 GHz, τf = −12.84 ppm/°C) were obtained when x = 0.04 sintered at 750 °C.

Phase assemblage and microstructures of Gd2Ti2-xZrxO7 (x = 0.1–0.3) pyrochlore glass-ceramics as potential waste forms for actinide immobilization

Glass-ceramics (GCs) based on titanate pyrochlores have attracted recent attention as candidate waste forms for actinide immobilization. As zirconate pyrochlore has a superior radiation resistance, it is anticipated that Zr substitution of Ti in titanate pyrochlore GCs would increase their potential for waste form applications. The concept was primarily addressed via the preparation of Gd2Ti2-xZrxO7 (x = 0.1–0.3) GCs to determine the effects of sintering temperature, Zr substitution, and pyrochlore content (50–70 wt%) on the properties of the resultant GCs. XRD and SEM analyses were used to reveal the phase assemblages and microstructures while TEM and Raman spectroscopy were used to analyze the local structures. XRD results confirmed the formation of the targeted pyrochlore as the major phase, with Gd9.33(SiO4)6O2 oxyapatite present as a minor phase. SEM analyses revealed that up to 0.2 formula units of Ti could be substituted by Zr under the processing conditions. The pyrochlore crystallite sizes were largely controlled by the sintering temperature and cooling rate and showed little sensitivity to the glass contents. This work has demonstrated successful substitutions of Ti with Zr in Gd2Ti2O7 GCs as potential waste forms for actinide wastes owing to their superior radiation resistance.

Enhanced Electrochemical Performance of the Fe-Based Layered Perovskite Oxygen Electrode for Reversible Solid Oxide Cells

Reversible solid oxide cells (RSOCs) present a conceivable potential for addressing energy storage and conversion issues through realizing efficient cycles between fuels and electricity based on the reversible operation of the fuel cell (FC) mode and electrolysis cell (EC) mode. Reliable electrode materials with high electrochemical catalytic activity and sufficient durability are imperatively desired to stretch the talents of RSOCs. Herein, oxygen vacancy engineering is successfully implemented on the Fe-based layered perovskite by introducing Zr4+, which is demonstrated to greatly improve the pristine intrinsic performance, and a novel efficient and durable oxygen electrode material is synthesized. The substitution of Zr at the Fe site of PrBaFe2O5+δ (PBF) enables enlarging the lattice free volume and generating more oxygen vacancies. Simultaneously, the target material delivers more rapid oxygen surface exchange coefficients and bulk diffusion coefficients. The performance of both the FC mode and EC mode is greatly enhanced, exhibiting an FC peak power density (PPD) of 1.26 W cm-2 and an electrolysis current density of 2.21 A cm-2 of single button cells at 700 °C, respectively. The reversible operation is carried out for 70 h under representative conditions, that is, in air and 50% H2O + 50% H2 fuel. Eventually, the optimized material (PBFZr), mixed with Gd0.1Ce0.9O2, is applied as the composite oxygen electrode for the reversible tubular cell and presents excellent performance, achieving 4W and 5.8 A at 750 °C and the corresponding PPDs of 140 and 200 mW cm-2 at 700 and 750 °C, respectively. The enhanced performance verifies that PBFZr is a promising oxygen electrode material for the tubular RSOCs.

New ionic conductor: Ba-deficient Ba3Y4O9 with Zr substitution

To lower operating temperatures of solid oxide fuel cells (SOFCs), the development of ion-conducting oxides with high conductivity and durability is desired. In this work, we investigated Zr-substituted “Ba3Y4O9” as an ionic conductor at intermediate temperatures and found that the Zr substitution for Y dramatically improves the phase stability in humidified atmospheres at 300–800 °C. The total electrical conductivity of nominally 20 mol% Zr-substituted Ba3Y4O9 sample is about 0.1 mS/cm at 500 °C in both dry H2 and O2 atmospheres. Because an increase in the conductivity in a humidified atmosphere was not observed, the conducting carriers may be oxygen ions. Besides, in the Zr-substituted “Ba3Y4O9” samples, we observed that BaO-rich phase coexists with the main phase whose composition is estimated to be Ba:(Y + Zr) ~ 2:3. Therefore, the main conducting phase might be Ba-deficient Ba3Y4O9. The mechanism of the ionic conduction and the improvement of chemical stability has not been revealed yet due to the lack of crystallographic information about the Ba-deficient phase. While we are now working on further investigation, we promptly report the characteristic of the new compound.

Stabilization of charged substitutional ions in tetragonal zirconia

The formation of substitutional and interstitial diluted defects of tantalum, niobium and molybdenum in a tetragonal zirconia (T-ZrO2) crystal was studied with Density Functional Theory calculations. Bader charge analysis was used to select the oxidation states (OS) which reached electronic localization around the substitutional ion. Oxidation states from +5 to +3 for Nb, +6 to +2 for Mo and +5 to +3 for Ta substitution ions were selected and formation energies were calculated. The work is focused on substitutional defects, after confirmation that substitutional defects produce higher stability than interstitial ones. Comparing the whole calculation set, it was found that Ta charge defects with oxidation state +5 (TaZr∗) exhibiting less available electrons than the replaced Zr ion, presented the minimum formation energy. Kröger-Vink diagrams evidence that TaZr∗has indeed the lowest formation energy values over the entire range of electron chemical potential. Electronic redistribution due to the substitution of Zr by a charged Ta ion results in an enhanced covalent bond between Ta and nearest O ions and charge polarization between Ta ion and the next nearest O ions along 〈111〉 and <11-1> directions. The results are of great technological incidence, asserting that Ta addition to zirconium nuclear alloys could improve its corrosion resistance properties.

Effects of Al replacement on glass forming ability and mechanical properties of Zr-based bulk metallic glasses

In this present study, the effects of Al substitution for Zr in Zr73-xCu12Ni12AlxNb3 (x=7.5, 10, 12.5, 15, 17.5 at.%) metallic glasses on the glass-forming ability, thermal stability, quasi-static and dynamic mechanical properties were investigated. Proper Al replacement improved the glass-forming ability, crystallization activation energy and mechanical properties of the amorphous alloys. Compared with quasi-static compression, due to the shorter loading time and more significant adiabatic temperature rise, the fracture strength decreased and no dynamic compression plasticity was observed for all alloys subjected to dynamic loading. From the aspect of atomic structure, the substitution of appropriate amount of Al not only promoted the formation of the stable short-range ordering (SRO) structure, but also changed the content and distribution of the free volume, which resulted in the improvement of GFA, strength and plasticity of the amorphous alloy.

Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li3–xIn1–xZrxCl6 (0 ≤ x ≤ 0.5)

In recent years, ternary halides Li3MX6 (M = Y, Er, In; X = Cl, Br, I) have garnered attention as solid electrolytes due to their wide electrochemical stability window and favorable room-temperature conductivities. In this material class, the influences of iso- or aliovalent substitutions are so far rarely studied in depth, despite this being a common tool for correlating structure and transport properties. In this work, we investigate the impact of Zr substitution on the structure and ionic conductivity of Li3InCl6 (Li3–xIn1–xZrxCl6 with 0 ≤ x ≤ 0.5) using a combination of neutron diffraction, nuclear magnetic resonance, and impedance spectroscopy. The analysis of high-resolution diffraction data shows the presence of an additional tetrahedrally coordinated lithium position together with a cation-site disorder, both of which have not been reported previously for Li3InCl6. This Li+ position and cation disorder lead to the formation of a three-dimensional lithium-ion diffusion channel, instead of the expected two-dimensional diffusion. Upon Zr4+ substitution, the structure exhibits nonuniform volume changes along with an increasing number of vacancies, all of which lead to increasing ionic conductivity in this series of solid solutions.

Effect of the addition mechanism of ZnO sintering aid on densification, microstructure and electrical properties of Ba(Zr,Y)O3-δ proton-conducting perovskite

We explore three different potential mechanisms to introduce 4 mol% ZnO sintering additive to the promising yttrium-doped barium zirconate (Ba(Zr,Y)O3-δ, BZY) proton conductor. The mechanisms involve Zn substitution for Y, Zr, or B-site cation excess. The addition of ZnO promotes high densification levels (up to 98% of the theoretical value) at 1300 °C, irrespective of the mechanism. However, scanning electron microscopy shows that the B-site cation excess mechanism leads to an impaired grain growth compared to the other mechanisms. Rietveld refinement of the lattice-parameters and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy indicates that Zn resides in both grains and grain boundaries in all cases. Determination of partial conductivities demonstrates that the Zr substitution mechanism provides slightly higher values of bulk protonic conductivity, as well as a higher hydration enthalpy. In contrast, the B-site excess mechanism provides the highest specific grain-boundary conductivity, as a result of greater Zn segregation to the grain boundary.

Synthesis, Characterization, and Hydrogen Isotope Storage Properties of Zr1-x Ti x Co and Zr1-x Hf x Co Alloys (x = 0.1, 0.2)

In the present study, the effect of Hf and Ti substitution of Zr in the ZrCo alloy, used for hydrogen isotope storage, has been investigated in order to ascertain the improvement of the anti-disproportionation property of ZrCo hydrides. The ultimate goal of the investigation is to develop a safe and economically viable solution for the long-term storage of deuterium and tritium. The intermetallic compounds Zrl-xTixCo and Zrl-xHfxCo (x = 0.1, 0.2) were prepared and their suitability for hydrogen isotope storage, protium (H) and deuterium (D), was investigated. The alloys were synthesized by arc melting under a controlled argon atmosphere and characterized by scanning electron microscope and X-ray diffraction analysis. The hydrogen isotope storage behavior of these alloys was probed by loading and unloading protium and deuterium. We present the pressure, composition, and temperature measurements for desorption, together with the thermodynamic parameters (enthalpy and entropy) of these alloys. The experimental results show that Ti and Hf substitution in the ZrCo alloys is suitable for fast delivery of hydrogen isotopes, even after their long-term storage.

DLC coated spur gears – Part II: coating properties and potential for industrial use

PurposeThis paper aims to address the coating and compound analysis of diamond-like carbon (DLC) on steel, to understand the frictional behavior in tribological gear systems presented in paper Part I. Here, the Ti and Zr modified DLC coating architectures are analyzed regarding their chemical, mechanical and thermophysical properties. The results represent a systematic analysis of the thermal insulating effect in tribological contact of DLC coated gears.Design/methodology/approachThe approach was to evaluate the effect of the substitution of Zr through Ti at the reference coating ZrCg to TiCg and the effect on thermophysical properties. Furthermore, the influence of different carbon and hydrogen contents on the coating and compound properties was analyzed. Therefore, different discrete Ti or Zr containing DLC coatings were deposited on an industrial coating machine. Thereby the understanding of the microstructure and chemical composition of the reference coatings is increased.FindingsResults prove comparable mechanical properties of metal modified DLC independent of differences in chemical compositions. Moreover, the compound adhesion between TiCg/16MnCr5E was improved compared to ZrCg/16MnCr5E. The effect of hydrogen content Ψ and carbon content xc on the thermophysical properties is limited by Ψ = 18 at.% and xc = 90 at.%.Practical implicationsThe findings of the combined papers Part I and II show a high potential for industrial application of DLC on gears. Based on the results DLC coatings and gears can be tailored to each other.Originality/valueSystematic analysis of DLC coatings were conducted to evaluate the effect of titanium, carbon and hydrogen on thermophysical properties.