Surface modification of Zr-based bulk amorphous alloys by using ion irradiation

Surfaces of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈M₂ (M = Er and Gd) bulk amorphous alloys were modified by irradiation with energetic singly charged argon (Ar⁺) ions. Samples of both the alloys were irradiated with 2.17 × 10¹⁷ argon ions of 10 keV energy. As cast and ion irradiated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Mechanical properties like Vicker's hardness, nanohardness, elastic modulus and elastic recovery were measured. Considerable increase in elastic modulus and hardness was observed because of ion irradiation in these alloys. The ion irradiated samples of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Er₂ alloy showed better properties as compared to [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Gd₂ alloy. CuZr₂ phase was detected in ion irradiated alloys by XRD and confirmed by EDS. The range of Ar⁺ ions was found to be approximately 9.3 ± 5.4 nm in both alloys.     

Anisotropic nanocrystallization of a Zr-based metallic glass induced by Xe ion irradiation

Structural modification in a Zr-based metallic glass caused by irradiation with 7 MeV Xe²⁶⁺ ions was investigated. Needle-like nanocrystalline structures, formed under ion irradiation, consist of Cu₁₀Zr₇ phase (primary) and/or minor (Ni_xCu_1−x)₁₀Zr₇ phase. The formation of needle-like nanocrystals suggested an anisotropic atomic diffusion caused by ion irradiation.     

Electron irradiation induced phase transformation in Zr66.7Cu33.3 and Zr66.7Pd33.3 metallic glass

Crystallization and phase selection in Zr_66.7Cu_33.3 and Zr_66.7Pd_33.3 metallic glass during thermal annealing and electron irradiation were examined. During thermal annealing an equilibrium C11_b–Zr₂Cu phase directly precipitated in the amorphous phase of Zr_66.7Cu_33.3 metallic glass while a thermal equilibrium C11_b–Zr₂Pd phase formed after icosahedral quasi-crystalline phase precipitation in Zr_66.7Pd_33.3 metallic glass. The amorphous phase was not stable under electron irradiation and metastable crystalline phases with face-centered cubic-based structure formed in both kinds of metallic glass by electron irradiation induced crystallization. The unique phase selection in electron irradiation induced crystallization is due to a change in the phase stability of crystal, quasi-crystal and amorphous phase under electron irradiation.     

Effect of CuO on the sintering temperature and piezoelectric properties of MnO2-doped 0.75Pb(Zr0.47Ti0.53)O3-0.25Pb(Zn1/3Nb2/3)O3 ceramics

The sintering temperature of 0.75Pb(Zr_0.47Ti_0.53)O₃-0.25Pb(Zn_1/3Nb_2/3)O₃ ceramics containing 1.5 mol% MnO₂ was decreased from 930 to 850 °C with the addition of CuO. The CuO reacted with the PbO and formed a liquid phase during the sintering, which assisted the densification of the specimens. Most of the Cu²⁺ ions existed in the CuO second phase, thereby preventing any possible hardening effect from the Cu²⁺ ions. Variations of the k_p, Q_m, ?₃^T/?₀ and d₃₃ values with CuO were similar to that of the relative density. The specimen containing 0.5 mol% CuO sintered at 850 °C showed the good piezoelectric properties of k_p = 0.5, Q_m = 1000, ?₃^T/?₀ = 1750 and d₃₃ = 300 pC/N.     

Structural and magnetic nanoclusters in Cu50Zr50−xGdx (x = 5 at.%) metallic glasses

It is shown that phase-separated metallic glasses on the nanoscale can be prepared by rapid quenching of Cu₅₀Zr_50−xGd_x melts with a low concentration of gadolinium (x = 5 at.%). Gd-enriched clusters of 2 nm size are formed as early stages of decomposition in the deeply undercooled melt. The key physical parameter to obtaining such a nanoclustered microstructure upon quenching is the critical temperature of liquid-liquid phase separation which has to be close to the glass transition temperature. Thus, the thermodynamic properties of the liquid phase even in the metastable deeply undercooled melt essentially determine the structure formation. Analysis of the spatial atomic arrangement by atom probe tomography after annealing in the supercooled liquid state provides direct evidence of the spinodal character of the decomposition by uphill diffusion. The Gd-enriched nanoclusters exhibit ferromagnetic ordering below 50 K and the cluster size regime derived from magnetization measurements is in good agreement with that obtained from atom probe tomography investigations. The first stage of crystallization of Cu₅₀Zr₄₅Gd₅ glass is observed to be Ostwald-type ripening on a nanoscale. The phase-separated glass acts as a precursor for the formation of a metastable nanocrystalline structure.     

Low temperature growth of nanocrystalline TiO2 films with Ar/O2 low-field helicon plasma

TiO₂ thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO₂ was obtained for ion density on the substrate below 7 × 10¹⁶ m^− 3. Increasing the ion density over 7 × 10¹⁶ m^− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO₂. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO₂ thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.     

Nanocrystallization-induced large room-temperature compressive plastic strain of Ti40Zr25Ni8Cu9Be18 BMG

By combining neutron diffraction, high-resolution transmission electron microscopy and thermal analysis measurements, the microstructure of as-cast Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ BMG with diameter of 2 mm was identified to be quenched-in nuclei/amorphous matrix. The quenched-in nuclei transform to (Ti,Zr)Be₂ nanocrystals with the average size of 4 nm homogeneously distributed into the amorphous matrix during deformation, which could be responsible for the large room-temperature compressive plastic strain, up to 8.0% at a constant strain rate of 5 × 10⁻⁴ s⁻¹.     

Preparation, structure and electrical conductivity of the pyrochlore-type phase Sm2Zr2O7 codoped with bivalent magnesium and trivalent dysprosium cations

The pyrochlore-type phases with the compositions of SmDy_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.20) have been prepared by pressureless-sintering method for the first time as possible solid electrolytes. The structure and electrical conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics have been studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy measurements. SmDy_1−xMg_xZr₂O_7−x/2 (x = 0, 0.05, 0.10) ceramics exhibit a single phase of pyrochlore-type structure, and SmDy_1−xMg_xZr₂O_7−x/2 (x = 0.15, 0.20) ceramics consist of pyrochlore phase and a small amount of the second phase magnesia. The total conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics obeys the Arrhenius relation, and the total conductivity of each composition increases with increasing temperature from 673 to 1173 K. SmDy_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest total conductivity value is about 8 × 10⁻³ S cm⁻¹ at 1173 K for SmDy_1−xMg_xZr₂O_7−x/2 ceramics.     

Nanocrystalline Zr3Al made through amorphization by repeated cold rolling and followed by crystallization

The intermetallic compound Zr₃Al is severely deformed by the method of repeated cold rolling. By X-ray diffraction it is shown that this leads to amorphization. TEM investigations reveal that a homogeneously distributed debris of very small nanocrystals is present in the amorphous matrix that is not resolved by X-ray diffraction. After heating to 773 K, the crystallization of the amorphous structure leads to a fully nanocrystalline structure of small grains (10-20 nm in diameter) of the non-equilibrium Zr₂Al phase. It is concluded that the debris retained in the amorphous phase acts as nuclei. After heating to 973 K the grains grow to about 100 nm in diameter and the compound Zr₃Al starts to form, that is corresponding to the alloy composition.     

Glass forming ability and crystallization of Zr-Cu-Ag-Al-Be bulk metallic glasses

The glass forming ability of Zr₄₆Cu_37.64−xAg_8.36Al₈Be_x (x = 0, 6 and 10 at.%) bulk metallic glasses (BMGs) were significantly improved by Be addition. The critical size of amorphous rods can be over 35 mm diameter. The high GFA achieved is mainly due to the decrease of melting point and liquidus temperature, and suppression of the formation of crystalline phases during solidification from liquid state. The high stabilization with supercooled liquid regime of 115 K was found for the BMG with x = 10 at.%. Two independent exothermic events happen in x = 0 and 6 at.% BMGs, corresponding to the formation of primary crystalline phases Cu₁₀Zr₇ and AgZr, then transforming to final stable crystalline phases Zr₂Cu and AlCu₂Zr. However, in the x = 10 at.% BMG, the precipitation of primary phases and transformation to final stable phases are within the first exothermic event and the AlCu₂Zr phase is totally suppressed.     

Unusual oxidation behaviour of Zr50Cu50 alloy at high temperatures

The oxidation of Zr₅₀Cu₅₀ alloy at 500-700 °C is characterized by preferential oxidation of zirconium, while the excess of copper is accumulated at the alloy-oxide interface forming the Zr₁₄Cu₅₁ phase. The strong reaction at 800 and 850 °C resulted in the total corrosion of the specimens in 21 and 15 h, respectively. The oxidation at elevated temperatures showed an anomalous decrease of the oxygen consumption rate in the temperature range 930-1000 °C, corresponding to the preferentially oriented crystallites of ZrO₂ in the oxide scale at 900 and 1000 °C. The oxide layer consists of ZrO₂ and CuO in the whole temperature interval of the oxidation. The reaction kinetics obeys a parabolic rate law. An activation energy of 92.0 ± 0.3 kJ/mol has been estimated.     

An in situ neutron diffraction study of the thermal disproportionation of the Zr2FeD5 system

The Zr₂FeD₅ system has been annealed to 680 °C under ultra high vacuum, and studied in situ by neutron diffraction. The system disproportionates through three distinct regions in temperature. Initially, the tetragonal Zr₂FeD₅ (P4/ncc) is retained up to 330 °C, while steadily depleted of D. From 330 °C to 530 °C, a complex multi-phase disproportionation occurs, with the production of cubic ZrD₂, tetragonal ZrD₂, tetragonal Zr₂FeD₅ (I4/mcm), and growth of the intermetallic ZrFe₂. At the beginning of the 330-530 °C period, the total atom count from quantitative phase analysis (QPA) indicates the formation of amorphous (a-) Zr₅₆Fe₄₄. By 530 °C, QPA and peak breadth analysis indicate that ca. 2/3rd of the sample is consumed as very small nanocrystals (<150 Å coherence length) of strained ZrD₂. From 530 °C to 680 °C, the cubic ZrD₂ is almost entirely consumed and depleted of D to form the final mixture of the intermetallic phases Zr₃Fe and ZrFe₂. QPA of the final intermetallic mixture yields a Zr:Fe ratio greater than that observed in either the arc melted alloy or the initial Zr₂FeD₅ deuteride, indicating that a ca. Zr₇₁Fe₂₉ amorphous component was present in the initial arc melted alloy. According to the total atom count by QPA, crystallisation of the Fe richer amorphous Zr₅₆Fe₄₄ phase formed at 330 °C begins at ca. 530 °C, and later by 680 °C, all amorphous phases have completely crystallised to yield a 70.77:26.75:2.47 mol.% mixture of Zr₃Fe:ZrFe₂:ZrD_2−x.     

Effect of ZrO2 addition on the microstructure and electromagnetic properties of YIG

In this work, we reported the microstructure and electromagnetic properties of a series of zirconium substituted yttrium iron garnet ferrites (YCaZrIG) with iron deficiency composition of Y_3−xCa_xZr_xFe_4.93−xO₁₂ (x = 0.1, 0.2, 0.3, and 0.4, with electrostatic balance by Ca²⁺ substituted for Y³⁺ ions) prepared by a solid-reaction method. The addition of ZrO₂ shows no obvious influence on the phase, density and dielectric constant of YIG ferrites. When Zr addition x ≤ 0.3, the substitution of Zr⁴⁺ for Fe³⁺ decreases the amount of Fe ions, increases the lattice parameter and enhances the grain growth of garnet phase. The solubility of zirconium in YCaZrIG ferrite was found to be approximately 0.3, above which excess ZrO₂ would lead to the precipitation of a second phase inside the YCaZrIG ferrite. This would inhibit the grain growth of garnet phase and cause an increase in the dielectric loss and coercivity. The observed reduce for saturation magnetization when x = 0.4 is possibly due to antiparallel alignment of magnetic moment of Fe³⁺ in the d site caused by the decrease of a-d exchange interaction. Additionally, we got the optimum electromagnetic properties in the samples with x = 0.3: ?_r = 14.1, tan δ_e = 2.5 × 10⁻⁴, H_c = 47 A/m, 4πM_s = 1936 × 10⁻⁴T, ΔH = 7.1 KA/m.     

Structure and crystallization kinetics of a Cu50Zr45Ti5 glassy alloy

The crystallization kinetics and structure changes in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy on heating were investigated by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and differential isothermal calorimetry. The glassy phase in the Cu₅₀Zr₄₅Ti₅ alloy was crystallized forming Cu₁₀Zr₇ and CuZr₂ phases upon thermal annealing. The activation energy for crystallization obtained by the Arrhenius equation was 435 kJ/mol. The crystallization process took place by nucleation and growth mechanism, and an Avrami exponent of about 3.3 may indicate a three-dimensional interface-controlled growth of nuclei with a decreasing nucleation rate.     

Zr-based bulk glassy alloy with improved resistance to stress corrosion cracking in sodium chloride solutions

In order to evaluate stress corrosion cracking (SCC) susceptibility of Zr-based bulk glassy alloys and develop the BGAs with low susceptibility to SCC, the SCC behaviour of Zr₅₀Cu₄₀Al₁₀, Zr₅₀Cu₃₀Al₁₀Ni₁₀ and hypoeutectic Zr₇₀Cu₆Al₈Ni₁₆ BGAs in various environments including sodium chloride solution has been investigated using a slow strain rate technique at an initial strain rate of 5 × 10⁻⁶ s⁻¹. It is found, for the first time, that the Zr₇₀Cu₆Al₈Ni₁₆ BGA has no susceptibility to SCC in a 0.5 M NaCl solution. On the other hand, Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Al₁₀Ni₁₀ BGAs are highly susceptible to SCC in the NaCl solution, although they are not susceptible to SCC in de-ionized water, phosphate buffer, 0.5 M Na₂SO₄ and 0.5 M NaNO₃ solutions. The possible cause of the high susceptibility to SCC in the NaCl solution for the Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Al₁₀Ni₁₀ BGAs is discussed.     

Hydrothermal synthesis of Cu3(OH)2V2O7·nH2O nanoparticles and its application in lithium ion battery

Well crystallized copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles have been successfully synthesized by a simple hydrothermal method. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The composition of Cu₃(OH)₂V₂O₇·nH₂O was studied by thermal analysis (TG, DTA), which indicates that there are two molecules of water in a Cu₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Cu₃(OH)₂V₂O₇·2H₂O nanoparticles as positive electrode of lithium ion battery were studied by conventional charge/discharge tests at different current density, showing steady initial discharge platforms near 1.7 V. The first discharge capacity of Cu₃(OH)₂V₂O₇·2H₂O electrode arrives at 868 and 845 mAh g⁻¹ at current density of 0.01 and 0.02 mA cm⁻², respectively.     

High permittivity and low dielectric loss of the Ca1−xSrxCu3Ti4O12 ceramics

The Ca_1−xSr_xCu₃Ti₄O₁₂ (CSCTO) giant dielectric ceramics were prepared by conventional solid-state method. X-ray diffraction patterns revealed that a small amount of Sr²⁺ (x < 0.2) had no obvious effect on the phase structure of the CSCTO ceramics, while with increasing the Sr²⁺ content, a second phase of SrTiO₃ appeared. Electrical properties of CSCTO ceramics greatly depended on the Sr²⁺ content. The Ca_0.9Sr_0.1Cu₃Ti₄O₁₂ ceramics exhibited a higher permittivity (71,153) and lower dielectric loss (0.022) when measured at 1 kHz at room temperature. The ceramics also performed good temperature stability in the temperature range from −50 °C to 100 °C at 1 kHz. By impedance spectroscopy analysis, all compounds were found to be electrically heterogeneous, showing semiconducting grains and insulating grain boundaries. The grain resistance was 1.28 Ω and the grain boundary resistance was 1.31 × 10⁵ Ω. All the results indicated that the Ca_0.9Sr_0.1Cu₃Ti₄O₁₂ ceramics were very promising materials with higher permittivity for practical applications.     

Dependence of lattice distortion of monoclinic phase on film thickness in Pb(Zr0.58Ti0.42)O3 thin films

In this paper, the chosen composition of PZT film falls in rhombohedral phase region and the dependence of lattice distortion on film thickness in sol-gel derived Pb(Zr_0.58Ti_0.42)O₃ thin films was systematically investigated. The results confirm that the Pb(Zr_0.58Ti_0.42)O₃ films have monoclinic phase even though the composition falls in the rhombohedral phase region. The mixed textures of (1 0 0) and (1 1 1) occur in the PZT films. In the case of mixed textures, a method using ψ-scan XRD to characterize the phase type of Pb(Zr_0.58Ti_0.42)O₃ film is presented. It is found that the phase type of (1 0 0)-oriented grains is M_A phase, and that of (1 1 1)-oriented grains is M_B phase. Moreover, the lattice constants of both M_A and M_B phases are sensitive to the film thickness. The lattice distortion of monoclinic phase becomes smaller as film thickness increases.     

Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Effect of addition of Ba(W0.5Cu0.5)O3 in Pb(Mg1/3Nb2/3)O3-Pb(Zn1/3Nb2/3)O3-Pb(Zr0.52Ti0.48)O3 ceramics on the sintering temperature, electrical properties and phase transition

In this work, we report on the Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramics with Ba(W_0.5Cu_0.5)O₃ as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W_0.5Cu_0.5)O₃ significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W_0.5Cu_0.5)O₃-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: (K_p = 0.63, Q_m = 1415 and d₃₃ = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications.