Nanocrystalline ZrO2 Research Articles

The Role of Oxygen Vacancies in Phase Transition and the Optical Absorption Properties within Nanocrystalline ZrO2.

Zirconia (ZrO2) nanoparticles were synthesized using a solvothermal method under varying synthesis conditions, namely acidic, neutral, and alkaline. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were leveraged to investigate the phase evolution and topographical features in detail. The resulting crystal phase structures and grain sizes exhibited substantial variation based on these conditions. Notably, the acidic condition fostered a monoclinic phase in ZrO2, while the alkaline condition yielded a combination of tetragonal and monoclinic phases. In contrast, ZrO2 obtained under neutral conditions demonstrated a refinement in grain sizes, constrained within a 1 nm scale upon an 800 °C thermal treatment. This was accompanied by an important transformation from a monoclinic phase to tetragonal phase in the ZrO2. Furthermore, a rigorous examination of XPS data and a UV-visible spectrometer (UV-vis) analysis revealed the significant role of oxygen vacancies in phase stabilization. The notable emergence of new energy bands in ZrO2, in stark contrast to the intrinsic bands observed in a pure monoclinic sample, are attributed to these oxygen vacancies. This research offers valuable insights into the novel energy bands, phase stability, and optical absorption properties influenced by oxygen vacancies in ZrO2. Moreover, it proposes an innovative energy level model for zirconia, underpinning its applicability in diverse technological areas.

Environmentally friendly production, characterization, and utilization of ZrO2 nanoparticles for the adsorption of amoxicillin in water solutions

Green synthesis is a viable alternative for creating nanoparticles from environmentally friendly sources. Sonchus asper extract was used in this study to prepare ZrO2 nanoparticles that can adsorb amoxicillin from an aqueous solution as a reducing and stabilizing agent. The complex product was synthesized and then annealed for four hours at 500 °C, 600 °C, and 700 °C to produce fine ZrO2 powder. X-ray diffraction, BET, FTIR, and TEM were employed to explore these samples' structural characteristics. Structural analyses showed that a cubic phase with slight size variation at different annealing temperatures is present in nanocrystalline ZrO2 powder. We examined the influence of initial amoxicillin concentration, pH, and temperature on amoxicillin adsorption. Compared with other widely popular materials used to remove amoxicillin, the zirconia produced in this study had a much better adsorption capability. The adsorption processes were spontaneous and endothermic, following thermodynamic characteristics, including standard enthalpy change (H), Gibb's free energy change (G), and standard entropy change (S). The green production method and zirconia nanoparticles are promising to adsorb a developing contaminant.

Study on dielectric relaxation and current–voltage characteristics of Mn-doped ZrO2 nanocrystalline solid solution at and above room temperature

Study on dielectric relaxation and current–voltage characteristics of Mn-doped ZrO2 nanocrystalline solid solution at and above room temperature

Structural and photoluminescence properties of Dy-doped nanocrystalline ZrO2 for optoelectronics application

Nanocrystalline Dy3+ doped ZrO2 sample has been synthesized using sol-gel wet chemical method. The sample has been investigated for structural, thermal, and photoluminescence properties employing X-ray Diffraction, Fourier Transform Infrared spectroscopy, Thermogravimetric analysis, Transmission Electron Microscopy, UV–visible spectroscopy, and Photo-Luminescence characterization techniques, respectively. The Rietveld refinement of XRD data reveals cubic phase (lattice constant = 5.138 Å) of doped-ZrO2 nano-crystals with space group Fm-3m. The average crystallite size and micro-strain are estimated as 46.21 nm and 0.0047, respectively, from Williamson-hall (W–H) plot analysis. FT-IR spectroscopy confirms the existence of Zr–O vibration modes of ZrO2 phase. The optical band gap of Dy-doped ZrO2 sample is found as 5.3 eV which is analogous to other reports. Photo-Luminescence result shows that the Dy doped-zirconia contains three significant characteristic peaks at 484, 583 and 678 nm under the excitation of a wavelength of 350 nm. Those peaks attribute to the electronic transition of Dy ions. The obtained CIE chromaticity coordinate of doped ZrO2 is (0.337, 0.335) representing neutral white light. The findings of this work implies application of doped zirconia in the area of optoelectronic devices.

Dynamics Of Structural-Phase States of Nanocrystalline ZrO2(CaO) During Sintering in a Constant Magnetic Field

Dynamics Of Structural-Phase States of Nanocrystalline ZrO2(CaO) During Sintering in a Constant Magnetic Field

Local Epitaxial Templating Effects in Ferroelectric and Antiferroelectric ZrO2.

Nanoscale polycrystalline thin-film heterostructures are central to microelectronics, for example, metals used as interconnects and high-K oxides used in dynamic random-access memories (DRAMs). The polycrystalline microstructure and overall functional response therein are often dominated by the underlying substrate or layer, which, however, is poorly understood due to the difficulty of characterizing microstructural correlations at a statistically meaningful scale. Here, an automated, high-throughput method, based on the nanobeam electron diffraction technique, is introduced to investigate orientational relations and correlations between crystallinity of materials in polycrystalline heterostructures over a length scale of microns, containing several hundred individual grains. This technique is employed to perform an atomic-scale investigation of the prevalent near-coincident site epitaxy in nanocrystalline ZrO2 heterostructures, the workhorse system in DRAM technology. The power of this analysis is demonstrated by answering a puzzling question: why does polycrystalline ZrO2 transform dramatically from being antiferroelectric on polycrystalline TiN/Si to ferroelectric on amorphous SiO2/Si?

On the role of stress in microstructure evolution during thermo-chemical surface engineering

<h2>Abstract</h2> Thermochemical surface engineering of metals is the deliberate and targeted modification of the (sub-)surface region of metals, with the aim to improve materials performance. Generally, thermochemical surface engineering is understood in terms of thermodynamics and diffusion kinetics to describe the evolution of the microstructure during chemical modification at elevated temperature. Associated with the change in composition, strains and stresses are introduced. These strains/stresses affect the thermodynamics and the kinetics of microstructure evolution. This contribution illustrates several examples from activities in the authors' research group. The following examples are covered:<ul><li>•The dissolution of nitrogen (N) or carbon (C) into austenitic stainless steels and high entropy alloys at temperatures below 725 K for N and below 825 K for C. Strong supersaturation with interstitials of the austenite leads to lattice expansion which is accommodated elasto-plastically and residual stresses of several GPas.</li><li>•Oxidizing of ZrCuAl-based bulk metallic glass (BMG) below the glass transition temperature leads to an internal oxidation zone (IOZ), consisting of nano-crystalline ZrO₂. Compressive residual stresses induce outward diffusion of "noble" elements, as for example Ag (if present) and Cu, which segregate at free surfaces. This segregation leads to crystalline metallic regions, which can provide a mechanism for self-healing of cracks.</li></ul>

Effect of Heat Treatment in the Temperature Range 400−1300°C on the Properties of Nanocrystalline ZrO2−Y2O3−CeO2 Powders

Effect of Heat Treatment in the Temperature Range 400−1300°C on the Properties of Nanocrystalline ZrO2−Y2O3−CeO2 Powders

Phase transformation and enhanced blue photoluminescence of zirconium oxide poly-crystalline thin film induced by Ni ion beam irradiation

Swift heavy ions (SHI) irradiation of Nickel (Ni) beam with different ions fluence bring the modifications in the functional properties of radio frequency (RF) grown zirconium oxide (ZrO2) nanocrystalline thin films. X-ray diffraction analysis affirms the monoclinic to tetragonal phase transformation and diminishing of peak at higher fluence 1 × 1014 and 2 × 1014 ions/cm2 induced by electronic excitation caused by SHI. Zirconium oxide thin films exhibit the same thickness (195 nm) of virgin and irradiated samples and whereas the nanocrystalline thin films have the elemental composition in proper stoichiometry (1:2) as analyzed by rutherford backscattering spectroscopy (RBS). Photoluminescence measurements confirm the blue emission of virgin and irradiated sample recorded at excitation wavelength 270 to 310 nm. The intensity of obtained emission bands varies with fluence which is interpreted in terms of generation and annihilation of defect centers. The characteristic Ag and Bg Raman modes of monoclinic and tetragonal ZrO2 are obtained at different positions. Moreover, the nanocrystalline ZrO2 thin films exhibits the most prominent absorption phenomenon in the visible range and the irradiation cause significant decrease in band gap to 3.69 eV compare to the virgin ZrO2 sample (3.86 eV). XPS analysis indicates the shifting of the core levels Zr 3d and O 1s towards higher binding energy and spin—orbit splitting of different states. The findings in this research justify that the irradiated thin films can be a potential candidate for designing of new materials, intense radiation environments, nuclear reactors, nuclear waste systems, clean energy sources.

Effects of atomic ordering of Zirconium oxide nanomodification on stem cell differentiation

The present study shows that the atomic ordering of ZrO2 thin films influences the osteoblastic differentiation of human mesenchymal stem cells (hMSCs). The amorphous ZrO2 film produced a better hMSCs response than the bare Ti surfaces, characterized by a higher production of osteoblastic markers, suggesting that amorphous ZrO2 coatings may enhance bone formation around implants. Slight differences were observed for the surface properties of amorphous and nanocrystalline ZrO2 thin films, being significant the larger barrier properties of the amorphous film.

Oxidation behavior of Al-Cr-Nb-Si-Zr high entropy nitride thin films at 850 °C

Oxidation behavior of Al-Cr-Nb-Si-Zr high entropy nitride (HEN) thin films was investigated in air atmosphere at 850 °C. The thermo-gravimetric analyzer (TGA) results show that oxidation kinetics of HEN films followed the parabolic rate law. A triple oxide layer, Al2O3/Cr2O3/Al2O3, was found with nanocrystalline ZrO2 dispersed in the oxide scales. Through Au nanoparticles as diffusion markers, the formation of the scales was mainly due to the outward diffusion of cations in the beginning, and the dominant diffusion species were changed to inward diffusion of anions in longer oxidation periods.

Microplotter-Printed On-Chip Combinatorial Library of Ink-Derived Multiple Metal Oxides as an "Electronic Olfaction" Unit.

Information about the surrounding atmosphere at a real timescale significantly relies on available gas sensors to be efficiently combined into multisensor arrays as electronic olfaction units. However, the array's performance is challenged by the ability to provide orthogonal responses from the employed sensors at a reasonable cost. This issue becomes more demanded when the arrays are designed under an on-chip paradigm to meet a number of emerging calls either in the internet-of-things industry or in situ noninvasive diagnostics of human breath, to name a few, for small-sized low-powered detectors. The recent advances in additive manufacturing provide a solid top-down background to develop such chip-based gas-analytical systems under low-cost technology protocols. Here, we employ hydrolytically active heteroligand complexes of metals as ink components for microplotter patterning a multioxide combinatorial library of chemiresistive type at a single chip equipped with multiple electrodes. To primarily test the performance of such a multisensor array, various semiconducting oxides of the p- and n-conductance origins based on pristine and mixed nanocrystalline MnOx, TiO2, ZrO2, CeO2, ZnO, Cr2O3, Co3O4, and SnO2 thin films, of up to 70 nm thick, have been printed over hundred μm areas and their micronanostructure and fabrication conditions are thoroughly assessed. The developed multioxide library is shown to deliver at a range of operating temperatures, up to 400 °C, highly sensitive and highly selective vector signals to different, but chemically akin, alcohol vapors (methanol, ethanol, isopropanol, and n-butanol) as examples at low ppm concentrations when mixed with air. The suggested approach provides us a promising way to achieve cost-effective and well-performed electronic olfaction devices matured from the diverse chemiresistive responses of the printed nanocrystalline oxides.

Structure and behavior of ZrO2-graphene-ZrO2 stacks

ZrO2-graphene-ZrO2 layered structures were built and their crystallinity was characterized before resistive switching measurements. Thin nanocrystalline ZrO2 dielectric films were grown by atomic layer deposition on chemical vapor deposited graphene. Graphene was transferred, prior to the growth of the ZrO2 overlayer, to the ZrO2 film pre-grown on titanium nitride. Nucleation and growth of the top ZrO2 layer was improved after growing an amorphous Al2O3 interface layer on graphene at lowered temperatures. Studies on resistive switching in such structures revealed that the exploitation of graphene interlayers could modify the operational voltage ranges and somewhat increase the ratio between high and low resistance states.

Strain, stress and stress relaxation in oxidized ZrCuAl-based bulk metallic glass

Surface engineering of Zr51.3Al8.5Cu31.3Ni4Ti4.9 bulk metallic glass (BMG) by gaseous oxidizing below the glass-transition temperature is investigated as a means to introduce compressive residual stress in the surface region. The ZrCuAl-based BMG was exposed to an extremely low oxygen partial pressure of 10−41 bar at 600 K for 60 h. The oxidizing treatment led to the formation of an internal oxidation zone, consisting of finely dispersed nano-crystalline cubic ZrO2 (c-ZrO2), metallic regions inclined with the surface and Cu-hillocks at the surface. The stresses introduced by the volume expansion associated with oxidation were evaluated from i) the lattice strains within c-ZrO2, as determined with an X-ray diffraction (XRD) based method, and ii) strain-relaxation as a response to annular focused ion beam (FIB) milling, as monitored with digital image correlation (DIC). XRD analysis yielded -1.5 GPa (compressive stress) in the nano-crystalline c-ZrO2, while the strain relaxation monitored with FIB-DIC analysis indicated compressive residual stresses of −1.4 GPa in the internal oxidation zone. The strains and stresses determined with the independent measurement methods are discussed. The quantitative macro-strains are discussed in relation to the microstructural features and stress relaxation mechanisms during evolution of the internal oxidation zone.

Synthesis and Luminescent Properties of Nanocrystalline (1 – х)ZrO2–хEr2O3 (х = 0.015–0.5) Solid Solutions

Efficient method for the directed synthesis of ZrO2–Er2O3 luminescent material in nanocrystalline state has been developed. Monodisperse samples of cubic modification with particle size from 5 to 71 nm depending on synthesis conditions have been synthesized. Luminescence spectra due to 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 transitions of Er3+ ions have been registered upon their excitation by 532-nm radiation. Upconversion luminescence spectra due to 2H11/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 transitions have been registered on excitation to level 4I13/2 of Er3+ ions by 1550-nm radiation.

Experimental evidences of ferromagnetism in undoped monoclinic zirconia

Mixed magnetic feature of paramagnetism and ferromagnetism at room temperature has been observed in annealed powders of nanocrystalline zirconia within a temperature range of 650 °C to 1050 °C. The abundant defect states such as, oxygen vacancies and clusters are originated during the synthesis process. The long range ferromagnetism in nanocrystalline ZrO2 is also due to exchange interaction between the various charge state of oxygen vacancies present at the surface or bulk of the nanostructure and the reduced Zr 4d ions, which leads to the creation of bound magnetic polaron at the defect area in the system. It is also observed that both the zero field curve (ZFC) and field cooled (FC) curve runs simultaneously from room temperature to 50 K without having any significant change in irreversibility temperature.

Preparation of tetragonal zirconia microspheres as surrogate precursor for uranium nitride microspheres

Zirconia (ZrO2) microspheres are of great interest as a surrogate precursor material for preparation of uranium nitride (UN) microspheres in High Temperature Reactor (HTR). However, the crystallite transformation of ZrO2 microspheres in cooling process causes cracking of the microspheres. In our study, crack-free nanocrystalline ZrO2 microspheres were obtained. The tetragonal phase was stabilized at room temperature without doping any stabilizing additives. Firstly, gel microspheres were prepared through internal gelation process. Subsequent heat treatment of gel microspheres in nitrogen was conducted. The effect of heat treatment was investigated by using simultaneous thermogravimetric analysis and differential scanning calorimetric analysis (TGA/DSC). By using X-ray diffraction (XRD), optical microscopy, and field-emission scanning electron microscopy (FE-SEM), the phase compositions, morphology and microstructures of the heat treated microspheres were characterized. The ZrO2 microspheres treated at 800 °C exhibit room-stabilized tetragonal zirconia phase, with uniform size of 650 ± 15 μm, good sphericity of 1.02 ± 0.01, and relatively high crush strength 122.5 ± 13.8 N/sphere. Finally, a preliminary nitridation was conducted. Those room-stabilized tetragonal zirconia microspheres can be used as a good surrogate precursor for subsequent preparation of nitride microspheres.

Phase transformation and modifications in high-k ZrO2 nanocrystalline thin films by low energy Kr5+ ion beam irradiation

In present communication, zirconium oxide (ZrO2) thin films of thickness (155 nm) were grown by using RF sputtering technique. To address and systematically understand the effects of low energy (800 keV) irradiation, high-k ZrO2 thin films were irradiated at room temperature by Kr ions with a range of fluence 1E15 to 1E17 ions. cm−2. The polymorphous zirconia pristine and irradiated thin films were characterized through X-ray diffraction (XRD) technique which confirms the coexistence of monoclinic and tetragonal phases. Monoclinic to tetragonal structural phase transformation was observed for Kr5+ ions irradiated samples at a fluence of 5E15, 1E16, 1E17 ions. cm−2. All samples were characterized by UV–Vis spectroscopy to study the mechanism of variation in optical energy band gap (4.42–4.52 eV), Urbach energy (402–449 meV) and refractive index (1.518–1.523) with increasing ion fluence. Photoluminescence (PL) spectroscopy was done at room temperature to record the significant PL broad prominent emission peaks at 350 nm and 430 nm and the peak intensity of these peaks significantly varies due to the annihilation of primary defects or generation of new defects centres by the influence of Kr ion irradiation. To determine the significant variation in grain size (50–85 nm) and RMS surface roughness (0.54–1.04 nm), pristine and irradiated sample were characterized by atomic force microscopy (AFM). A complete mechanism of the evolution of surface roughness was analyzed by determining the power spectral density (PSD). Further surface roughness component in the range of 0.4–1.7 was calculated using the slope of the tail of PSD. The FTIR spectra of pristine and low energy ion irradiated ZrO2 thin films were recorded in the range of 1250–3200 cm−1. The Rutherford backscattering spectrometry (RBS) was carried out in channeling condition and the experimental results were simulated to evaluate the elemental composition of Zr and O (⁓1:2) and film thickness (155 nm) of the samples. The changes of the chemical binding energy of ZrO2 thin films of Zr 3d and O 1s region before and after ion irradiation were investigated by x-ray photoelectron spectroscopy (XPS).

Improvement in ferroelectricity of HfxZr1−xO2 thin films using top- and bottom-ZrO2 nucleation layers

A ferroelectric HfxZr1−xO2 (HZO) thin film crystallized with nanocrystalline top- and bottom-ZrO2 nucleation layers (D-ZrO2) exhibited superior remanent polarization (2Pr = Pr+ − Pr− = 29 μC/cm2) compared to that of similar thin films (12 μC/cm2) crystallized without a ZrO2 nucleation layer (w/o) when the HZO film thickness was 10 nm. Epitaxial-like grain growth of the HZO film was observed on the surfaces of both the top- and bottom-ZrO2 layers, while there was almost no significant difference in the crystal grain size of the HZO film in all samples, as determined by cross-sectional transmission electron microscopy images. Consequently, the ferroelectric orthorhombic, tetragonal, and cubic (O/T/C) phase ratio of the HZO film was significantly increased by using the ZrO2 nucleation layers. It was furthermore confirmed that the 2Pr values were strongly correlated with the O/T/C phase ratio of the HZO film. Therefore, it is clear that the top- and bottom-ZrO2 nucleation layers play an important role in the formation of the ferroelectric HZO film. These results suggest that the HZO film fabrication technique using a nanocrystalline ZrO2 nucleation layer is a promising candidate for next-generation device applications.

Phase composition and photoluminescence correlations in nanocrystalline ZrO2:Eu3+ phosphors synthesized under hydrothermal conditions

Phase composition and photoluminescence correlations in nanocrystalline ZrO2:Eu3+ phosphors synthesized under hydrothermal conditions