Heat treatment induced phase separation and phase transformation of ZrNxOy thin films deposited by ion plating

Nanocrystalline ZrN_xO_y thin films were deposited on p-type Si (100) substrates using hollow cathode discharge ion-plating (HCD-IP) and the films were annealed at 700 and 900 °C in the controlled atmosphere. The purpose of this study was to investigate the phase separation, phase transformation and the accompanying change of properties of the heat-treated ZrN_xO_y films deposited by ion plating. With the increase of oxygen flow rate ranging from 0 to 10 sccm, the primary phase of the as-deposited films evolved from ZrN to nearly amorphous structure and further to monoclinic ZrO₂ (m-ZrO₂). After heat treatment at 700 and 900 °C, phase transformation occurred in the samples deposited at 8 and 10 sccm O₂, where a stoichiometric crystalline Zr₂ON₂ was found to derive from m-ZrO₂ with dissolving nitrogen (m-ZrO₂(N)). The hardness of the ZrN_xO_y thin films could be correlated to the fraction of Zr₂ON₂ + m-ZrO₂. The film hardness decreased significantly as the fraction of ZrO₂ + Zr₂ON₂ exceeded ~ 60%, which was due to phase transition by increasing oxygen flow rate or phase transformation induced by heat treatment. The phase separation of m-ZrO₂ from ZrN with dissolving oxygen (ZrN(O)) may relieve the residual stress of the ZrN_xO_y specimens deposited at 5 and 8 sccm O₂, while direct formation of m-ZrO₂ increased the stress of the film deposited at 10 sccm O₂. On the other hand, the phase transformation from m-ZrO₂(N) to Zr₂ON₂ by heat treatment at both 700 and 900 °C may effectively relieve the residual stress of the ZrN_xO_y films.     

Mechanical properties and corrosion resistance of nanocrystalline ZrNxOy coatings on AISI 304 stainless steel by ion plating

Transition metal oxynitrides have become emerging decorative coating materials due to their adjustable coloration and high hardness and corrosion resistance. This research studied the effect of oxygen content on the coloration, mechanical properties and corrosion resistance of ZrN_xO_y thin films deposited on AISI 304 stainless steel using hollow cathode discharge ion plating (HCD-IP). The Zr/N/O ratios of the ZrN_xO_y films were determined using X-ray photoelectron spectroscopy (XPS). The color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue with increasing oxygen content. X-ray diffraction (XRD) patterns revealed that phase separation of ZrN and m-ZrO₂ occurred as the oxygen content reached 31.2 at.%. ZrN(O) (ZrN with dissolving oxygen) is dominant at oxygen content less than 18.1 at.%, while m-ZrO₂ phase was prevailed at oxygen content above 40.3 at.%. Phase separation lowered the hardness of the ZrN_xO_y films as the fraction of ZrO₂ was less than 40%. The residual stresses in ZrN phase was higher than that in ZrO₂, and the residual stress decreased for the specimen containing 30 to 37% ZrO₂. For the samples containing more than 44% ZrO₂, the average residual stress was close to that in ZrO₂ phase. The corrosion resistance was evaluated by salt spray test and potentiodynamic scan in two solutions: 0.5MH₂SO₄ + 0.05 M KSCN and 5% NaCl solutions. The results showed consistent trend in the two solutions. From the results of potentiodynamic scan, corrosion resistance increased as the packing density of the film increased, whereas the film thickness was not a crucial factor on corrosion current; moreover, the electrical conductivity of the film may be one of the significant factors in corrosion resistance. Results of salt spray tests suggested that the corrosion of ZrN_xO_y in NaCl may play an important role in corrosion resistance.     

Synthesis and characterization of nanocrystalline ZrNxOy thin films on Si by ion plating

Based on the optimum deposition conditions of ZrN thin film from our previous study, by varying oxygen flow rate ranging from 0 to 8 sccm, nanocrystalline ZrN_xO_y thin films were deposited on p-type (100) Si substrates using hollow cathode discharge ion-plating (HCD-IP) system. The objective of this study was to investigate the effect of oxygen content on the composition, structure and properties of the ZrN_xO_y thin films. The oxygen content of the thin film, determined using X-ray photoelectron spectroscopy (XPS), increased with increasing oxygen flow rate. As the oxygen content increased, the color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue, and the microstructure observed by scanning electron microscopy (SEM) varied from columnar structure to finer grains and finally flat and featureless structure. Phase separation of ZrN_xO_y to ZrN and monoclinic ZrO₂ was found from X-ray diffraction (XRD) patterns when the oxygen content was higher than 9.7 at.%. The hardness of the film slightly increased as the oxygen content was less than 9.7% and then decreased to 15.7 GPa, a typical hardness of ZrO₂ phase, as the oxygen content further increased. The total residual stress of the film was measured using an optical method, and the residual stresses of ZrN and ZrO₂ phases were determined separately using modified XRD sin²ψ method. The total stress was close to the stress in ZrN phase as the ZrO₂ fraction was less than 30%, and was close to that in ZrO₂ phase as the ZrO₂ fraction was over 30%. The electrical resistivity of the film increased significantly with the increase of oxygen content. The film properties showed consistent trend with phase separation. As the fraction of ZrO₂ phase was small, the apparent properties of the films were more close to those in ZrN. When ZrO₂ fraction was over 30%, the films mainly exhibited the properties of ZrO₂.     

Mechanochemical and volume combustion synthesis of ZrB2

Formation of ZrB₂ by volume combustion synthesis (VCS) and mechanochemical process (MCP) from ZrO₂-Mg-B₂O₃ was studied. Production of ZrB₂ by VCS in air occurred with the formation of side products, Zr₂ON₂ and Mg₃B₂O₆ in addition to MgO and ZrB₂. Zr₂ON₂ formation was prevented by conducting VCS experiments under argon. Wet ball milling was applied to the VCS products before leaching for easier removal of Mg₃B₂O₆ phase. MgO and Mg₃B₂O₆ were removed from wet ball-milled products by leaching in 5 M HCl for 2.5 h. In MCP, 30-hour ball milling was found to be sufficient for the formation of ZrB₂ with no minor phase formation. Leaching of MCP products in 1 M HCl for 30 min was sufficient to remove MgO. Complete conversion of ZrO₂ to ZrB₂ did not take place in both production methods, even with excess amounts of Mg and B₂O₃. Therefore, formed ZrB₂ contained residual ZrO₂.     

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.     

CVD deposition and characterization of coloured Al2O3/ZrO2 multilayers

Coloured Al₂O₃/ZrO₂ multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO₂ process used in the multilayer, with ZrCl₄ as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO₂ phases. However by adding a relatively small amount of AlCl₃ during such a process results in ZrO₂ layers being composed of predominantly tetragonal ZrO₂ phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO₂ phase seem to be less perfect with existence of larger grains of ZrO₂ which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al₂O₃ layers.It is believed that, in the studied Al₂O₃/ZrO₂ multilayers, the observed tetragonal ZrO₂ phase is the result of a size effect, where small enough ZrO₂ crystallites energetically favor the tetragonal phase. However as the ZrO₂ crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO₂ phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO₂ based ceramics.     

Structural and dielectric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition at low temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(1 0 0) substrates at a room temperature under the oxygen pressure of 1-10 Pa by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were then post-annealed below 200 °C in a rapid thermal process furnace in air for 20 min. The dielectric and leakage current properties of Bi₂Zn_2/3Nb_4/3O₇ thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited under 1 Pa oxygen pressure and then post-annealed at a temperature of 150 °C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10 kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi₂Zn_2/3Nb_4/3O₇ thin films deposited at low temperatures. Moreover, Bi₂Zn_2/3Nb_4/3O₇ thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1 × 10⁻⁷ A/cm² at an applied bias field of 300 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films are potential materials for embedded capacitor applications.     

High sintering resistance of a novel thermal barrier coating

Sintering resistance of a novel thermal barrier coating Nd_xZr_1 − xO_y with Z dissolved in, where 0 < x < 0.5, 1.75 < y < 2 and Z is an oxide of a metal selected from Y, Mg, Ca, Hf and mixtures thereof, was studied. The coatings of Nd_xZr_1 − xO_y and typical 7YSZ were deposited by electron beam physical vapor deposition (EB-PVD) and air plasma spray (APS). The samples with the coating system of EB-PVD Nd_xZr_1 − xO_y or 7YSZ overlaid onto a MCrAlY bond coat were cyclically sintered at 1107 °C for 706 hours. The freestanding coatings of EB-PVD Nd_xZr_1 − xO_y and 7YSZ were isothermally sintered at 1371 °C for 500 hours. The microstructure of EB-PVD Nd_xZr_1 − xO_y before and after the sintering was evaluated and compared with EB-PVD 7YSZ. The sintering resistance of freestanding APS Nd_xZr_1 − xO_y coating was also investigated after isothermal sintering at 1200 °C for 50 and 100 hours. The results demonstrated that the new coatings of Nd_xZr_1 − xO_y applied with both EB-PVD and APS have higher sintering resistance than EB-PVD and APS 7YSZ, respectively.     

Relationships between Zr substitution for Ti and microwave dielectric properties in Mg(ZrxTi1−x)O3 ceramics

The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(Zr_xTi_1−x)O₃(MZ_xT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(Zr_xTi_1−x)O₃ ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr⁴⁺ substitution in the B-site could increase density and grain size. An excess of Zr⁴⁺ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZ_xT ceramics. The temperature coefficient of resonant frequency (τ_f) of Mg(Zr_xTi_1−x)O₃ ceramics slightly increased with increasing Zr content, and the variation in τ_f was attributed to the formation of secondary phases.     

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.     

Oxygen partial pressure dependence of memory effect of sputtered nc-Al/α-Al2O3 thin films

Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al₂O₃) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al₂O₃ films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O₂. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al₂O₃ matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure.     

Effect of Ag-doping on crystal structure and high temperature thermoelectric properties of c-axis oriented Ca3Co4O9 thin films by pulsed laser deposition

Ag-doped Ca₃Co₄O₉ thin films with nominal composition of Ca_3−xAg_xCo₄O₉ (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca₃Co₄O₉ thin films could reach 0.73 mW m⁻¹ K⁻² at around 700 K, which was about 16% higher than that of the pure Ca₃Co₄O₉ thin film.     

The effects of temperature and composition on the thermal conductivities of [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ? x ? 1) solid solutions

The thermal conductivities of [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ? x ? 1) solid solutions are studied in this paper. The incorporation of ZrO₂ and CeO₂ in the solid solution decreases the thermal conductivity compared with their end members (YSZ and YDC). The thermal conductivities of the solid solutions show clearly different temperature dependences in the ZrO₂-rich (0 ? x ? 0.5) region and in the CeO₂-rich region (0.5 ? x ? 1). The composition and the temperature dependence of the thermal conductivities are discussed based on established phonon scattering theories. We have concluded that the composition dependence of the thermal conductivity of this system is mainly controlled by the mass difference between Zr⁴⁺ and Ce⁴⁺, while the thermal conductivity-temperature relationship is dominated by the randomness of the defect distribution.     

Preparation of nanometric CeO2–ZrO2–Nd2O3 solid solution and its catalytic performances

A kind of nanometric CeO₂–ZrO₂–Nd₂O₃ (CZN) solid solution for a carrier in the automotive three-way catalysts was synthesized by a coprecipitation method and characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and oxygen storage capacity (OSC). For the purpose of comparison, an unincorporated CeO₂–ZrO₂ (CZ) was also synthesized. The XRD measurements disclose the prepared CeO₂–ZrO₂–Nd₂O₃ have a face-centered cubic fluorite structure and nanoparticle sizes. According to the results of XPS, Nd³⁺ ions can enter the CZ lattice and form a homogenous solid solution. Oxygen storage capacity measurements reveal that CeO₂–ZrO₂–Nd₂O₃ display high oxygen mobility at a low temperature. The results of the activity tests show that the catalyst exhibits good three-way catalytic activity and fairly wide range of air-to-fuel ratios.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

Influence of O2/Ar flow ratio on the structure and optical properties of sputtered hafnium dioxide thin films

Hafnium dioxide (HfO₂) thin films were deposited on a quartz substrate by RF reactive magnetron sputtering. The influence of O₂/Ar flow ratio on the deposition rate, structure and optical properties of HfO₂ thin films were systematically studied using X-ray diffraction (XRD), scan electron microscopy (SEM) and UV-visible spectroscopy. The results show that the deposition rate decreases obviously when the O₂/Ar flow ratio increases from 0 to 0.25 and then, decreases little as the O₂/Ar flow ratio further increases to 0.50. The HfO₂ thin films prepared are all polycrystalline with a monoclinic phase. The thin film deposited with pure argon shows a preferential growth and has considerably improved crystallinity and much larger crystallite size. Meanwhile, after oxygen is introduced into the deposition, the thin films prepared have random orientation, weakened crystallinity and smaller crystallite size. The refractive index is higher for the thin film deposited without oxygen and increases as the O₂/Ar flow ratio increases from 0.25 to 0.50. The band gap energy of the thin film increases with an increasing O₂/Ar flow ratio.     

Structural investigations of YSZ coatings prepared by DC magnetron sputtering

(ZrO₂)_1−x(Y₂O₃)_x thin films were sputter-deposited from metallic targets in various reactive argon-oxygen gas mixtures. Structural investigations have been realised by X-ray Diffraction (XRD), Raman spectroscopy and Transmission Electron Microscopy (TEM). The coatings microstructure have been characterised by TEM and their morphology by Scanning Electron Microscopy (SEM) on brittle-fracture cross sections. Chemical compositions have been achieved by Electron Probe Micro-Analysis (EPMA) and by Energy Dispersive Spectroscopy (EDS). Finally, attention was paid to the film optical properties, as assessed via Optical Transmission Interferometry (OTI) as well as spectrophotometry.In a first part, we have studied the influence of the argon pressure on the chemical, structural and morphological properties of the coatings. In a second part, we have observed the effect of the yttria content on the structure of the films.     

SOLID SOLUTION BEHAVIOR OF Y2−x−yGdxEuyO3 NANOPOWDERS DURING PROCESS OF PREPARATION AND THEIR LUMINESCENCE PROPERTIES

用柠檬酸螯合法制备Y_2-x-yGd_xEu_yO₃纳米粉体(x+y≤ 2), 通过FTIR, XRD和SEM分析了制备过程中的物相变化以及pH值对粉体 形貌的影响. 测试了Y_2-x-yGd_xEu_yO₃ 晶格常数和晶胞体积, 分析了Gd与Eu在Y₂O₃中的固溶行为及其发光性能. 结果表明: 在pH<3的体系中制备Y_2-x-yGd_xEu_yO₃粉体较为适合, 经900 ℃煅烧2 h可完全合成出立方相的Y_2-x-yGd_xEu_yO₃; 在pH=1时, 加入少量乙二醇 (5%, 体积分数) 时得到粉体形貌最佳, 粒径约90 nm, 近球形. 样品的发光性能和Y, Gd的配比以及Eu的含量有关, 当化学配比为Y_0.2Gd_1.65Eu_0.15O₃时样品发光强度最高,y值超过0.15会发生浓度猝灭, 导致发光强度降低.     

Structural, optical and electrical properties of Mg-doped CuCrO2 thin films by sol-gel processing

CuCr_1−xMg_xO₂ (x = 0, 0.03, 0.05, 0.07) thin films were prepared on sapphire substrates by sol-gel processing. The effect of Mg concentrations on the structural, morphological, electrical and optical properties was investigated. Highly transparent ≧70% Mg-doped CuCrO₂ thin films with p-type conduction and semiconductor behavior were obtained. The microstructure of the systems was characterized by scanning electron microscopy and the roughness increased as the content of Mg increased. The photoluminescence spectra results indicated that it had a green luminescent emission peak at the 530 nm. In this paper, CuCr_0.95Mg_0.05O₂ film has the lowest resistivity of 7.34 Ω cm with direct band gap of 3.11 eV. In order to investigate the conduction mechanism, the energy band of the CuCrO₂ films is constructed based on the grain-boundary scattering.     

Crystalline phases and magnetic properties of Cu-Bi-Zn co-doped Co2Z ferrites

The effects of Cu, Bi and Zn substitutions on the crystalline phase and magnetic properties of hexagonal ferrites with a composition of 3(Ba_1−xBi_xO)2(Co_1−yCu_yO)12(Fe_2-(x/4)Zn_(x/4)O₃) were investigated. The results showed that the addition of Bi and Zn can significantly promote Z phase formation. The Z phase may be triggered to decompose into U and W phases resulting from the evaporation of Bi and segregation of Co-rich ferrites at high sintering temperatures for samples with large amounts of Bi and Zn. The initial permeability decreased with increasing x value because the Bi substitution promoted Z phase decomposition into U and W phases.