Yttria-stabilized Zirconia Substrates Research Articles

Crystallization and phase separation of tungsten oxide-bismuth vanadate amorphous film by annealing in air

A WO3-B1VO4 amorphous film grown on the (001) yttria-stabilized zirconia (YSZ) substrate was annealed at 600 °C in air. The microstructures evolution was investigated by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. After annealed, the amorphous composite film crystalized into monoclinic BiVO4 and orthorhombic WO3. B1VO4 epitaxially grew on the YSZ, forming the matrix, where part of small irregular WO3 grains were embedded in. Other large-sized sub-stoichiometric WO3-6 (0<δ<3) grains with stacking faults lay on the film surface, which may contribute to the compressed strain of BiVO4 matrix vertically. Compared to the typical vertical heteroepitaxial nanocomposite of WO3-B1VO4 film grown at 600 °C by pulsed laser deposition, in the annealed composite film, the vertical lattice mismatched strain at WO3/B1VO4 interface decreased and lead to the disappearance of metastable hexagonal WO3.

Influence of Substrate Orientation and Oxygen Partial Pressure on the Morphology, Structure, and Electrical Property of Epitaxial Indium Tin Oxide Films

Indium tin oxide (ITO, tin-doped indium oxide) has been widely used in optoelectronic and other research fields because of its excellent electrical conductivity. However, there is a lack of systemic research on the influence of crystal orientation on the electrical properties of epitaxial ITO films. In this work, the epitaxial ITO films were deposited on low index planes of yttria-stabilized zirconia substrates by direct current magnetron sputtering at different oxygen partial pressures ranging from 0 to 3 Pa. The carrier concentration of the ITO film decreased with the increase of the oxygen partial pressure and further leading to the increase of overall resistivity. In addition, we also found that the Hall mobilities of ITO (100) films rapidly decreased with the oxygen partial pressure, while the Hall mobilities of ITO (111) films remained unchanged. The anisotropy of the carrier mobility was the main factor for the resistivity difference of ITO films with different orientations at high oxygen partial pressure.

A novel Ag–CuAlO2 sealant for reactive air brazing of 3YSZ and AISI 310S

Based on reactive air brazing (RAB), we designed a new type of sealant (Ag–xCuAlO2) for joining 3 mol.% yttria-stabilized zirconia (YSZ) ceramics and AISI 310S stainless steel. The CuAlO2 content affected the wettability of the sealant on the YSZ surface, and the joints had a high shear strength when Ag–2 wt.%CuAlO2, which had a small contact angle on the YSZ substrate, was used as the sealant. In addition, the thickness of the oxide layer was reduced compared to that for the Ag–CuO sealant. The effects of the processing parameters on the microstructure and shear strength of the joints were investigated, and the as-brazed joints reached their highest shear strength (93.7 MPa) when brazed at 1040 °C for 30 min. After high-temperature oxidation at 800 °C for 200 h, the shear strength of the joints remained at 50 MPa, and no apparent change in the microstructure was observed, proving that the joints possessed excellent oxidation resistance.

Effects of strain on ultrahigh-performance optoelectronics and growth behavior of high-quality indium tin oxide films on yttria-stabilized zirconia (001) substrates

Effects of strain on ultrahigh-performance optoelectronics and growth behavior of high-quality indium tin oxide films on yttria-stabilized zirconia (001) substrates

Properties and Performance of Electrolyte Supported SOFCs with EB-PVD Gd-Doped Ceria Thin-Films

High temperature solid oxide fuel cell (SOFC) is regarded as a unique electrochemical device to convert the chemical energy of a large diversity of fuels into electricity and heat with high efficiency and low emission. The electrolyte-supported cell (ESC) design is proven to be one of the most feasible SOFC technologies for commercial applications. Thickness reduction of yttria stabilized zirconia (YSZ) electrolyte supports without sacrifice of mechanical strength is favorable for cell performance enhancement.In this work, dense gadolinium-doped ceria (GDC) thin-films with thickness in the range of 0.15-0.5 µm were fabricated as Sr-barrier layers on the cathode side, and as strength-balance and adhesion layer on the anode side by electron beam physical vapor deposition (EB-PVD) method. Replacing the state-of-the-art screen-printed GDC layers, the approach with YSZ substrate sandwiched in between two GDC thin-films was proposed not only to prevent the formation of interfacial secondary phase on the cathode side, but also to increase the overall robustness of ESCs. Investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), it was confirmed that 0.5 µm thick GDC thin-films were effective to suppress the formation of Sr-zirconate phase at the YSZ/GDC interface. In comparison to reference cells with screen-printed GDC layers, higher breaking loads were recorded on the cells with PVD-GDC thin-films by Ring-On-Ring bending tests, showing considerably improved mechanical properties. Current-voltage characteristics and electrochemical impedance spectroscopy demonstrated that the performance of the as-prepared ESCs with GDC thin-films was comparable to the reference cells. Operated at 860 °C, the ESC with 0.5 µm GDC thin-film outperformed other tested cells with 0.15 µm or 0.3 µm GDC layers, and delivered a power density of 0.55 W•cm-2 at a cell voltage of 0.7 V. The results achieved in this work can be considered as step stones for the further development of ESCs with reduced electrolyte thickness, sufficient robustness and improved performance.This work is financially supported by the German Ministry for Economic Affairs and Energy (BMWi) within the framework of the project “Kostenoptimierter Stack und verbessertes Offgrid-System (KOSOS)” with grant number of 03ETB005C.

Computational Predictions of Upscaling Solid Oxide Electrochemical Reactor Performances By Pillared Electrolyte | Electrode Interfaces

Increasing densities of electrode | electrolyte interfacial areas (and triple phase boundaries) of solid oxide fuel cells or electrolyzers (solid oxide electrochemical reactors, SOERs) offers one means of increasing performance, reproducibility and potentially decreasing cost. Three-dimensional (3D) structuring of those interfaces can be achieved by 3D printing, but modelling is required to optimize geometries. Using kinetic parameter values from the literature, COMSOL finite element software was used to predict effects of YSZ electrolyte (c.f. electrode) pillar geometries on SOER performance, relative to planar YSZ electrolytes. The modified geometries are based on yttria-stabilized zirconia (YSZ) electrolyte pillars on top of < 10 mm thick planar YSZ electrolyte, thereby increasing interfacial to geometric area ratios. Electrolyte layers have been inkjet printed on Ni(O)-YSZ substrate negative electrode precursors and porous lanthanum strontium manganite (LSM) positive electrode have been printed over the YSZ, after sequential sintering producing complete SOERs: H2O-H2 | Ni(O)-YSZ | YSZ-YSZ pillars | YSZ-LSM | LSM | O2.Results will be reported showing that despite interfacial electrode | electrolyte areas being up scaled by factors of 10-100 - depending on pillar diameter (5-50 mm) and height (15-150 mm) - current densities were predicted to increase by only 70-100% due to increased current path length along the pillars, which increases ohmic potential loss relative to the faradaic impedance. Hence, predictions of enhancement depend strongly on the kinetic parameters of the electrode material.

Epitaxial Growth of EuF2 and EuO Thin Films Based on Spontaneous Anion Diffusion from Substrates

We report the epitaxial growth of EuF2 (111) thin films on F-ion-conducting CaF2 (111) substrates. We achieved the fluorination of the Eu metal without introducing fluorination gas into the vacuum chamber during magnetron sputtering; instead, F atoms were supplied by the substrates. This growth method also allows EuO (100) epitaxial thin films to be fabricated on O-ion-conducting yttria-stabilized zirconia substrates. X-ray diffraction, transmission electron microscopy, and optical absorption spectra verified that the proposed method yields high-quality EuF2 and EuO thin films. Therefore, this study presents a novel thin-film growth method based on spontaneous anion diffusion from substrates.

Active participation of “inert” YSZ substrates on interface formation in [formula omitted]/YSZ heterostructures

The bulk and emerging interface properties of magnetite Fe3O4/YSZ(001) heterostructures grown by pulsed laser deposition are investigated. Fe3O4 thin films (4–38 nm) grow epitaxially in (111) orientation and undergo a Verwey transition at max. TV = 117±0.6K. Surprisingly, the formation of interfacial Fe2O3 phase is observed albeit the quasi-inert properties of yttrium-stabilized zirconia (YSZ). Possible mechanisms include either (i) thermodynamically induced interfacial redox reaction at the YSZ substrate surfaces or (ii) oxygen diffusion from the outside atmosphere, as YSZ is a very good oxygen ion conductor. Hence, substrate-assisted oxygen supply may enable the control of emerging interface functionalities.

Luminescent properties and X-ray imaging result of Lu2O3:Eu structured scintillation film on YSZ single crystal substrate by LCVD method

Micro-columnar structured europium doped lutecia (Lu2O3:Eu) scintillation film is one of the most attractive candidate materials for high-energy hard X-ray imaging detectors because of their excellent physical, scintillation properties and light guide effect. Lu2O3:Eu micro-columnar film (MCF) with 9 μm thickness was obtained on a yttrium stabilized zirconia (YSZ) (100) single crystal substrate by laser chemical vapor deposition (LCVD), and its structure, morphology, photoluminescence and scintillation properties were characterized. The structure and morphology of obtained film were investigated by grazing incidence X-ray diffraction (GIXRD) and scan electron microscopy (SEM). The photoluminescence and scintillation properties, including photoluminescence excitation (PLE), photoluminescence (PL), PL decay, X-ray excited luminescence (XEL), were measured and discussed. The X-ray imaging result of Lu2O3:Eu MCF on YSZ substrate was obtained for the first time and spatial resolution of 2 μm was obtained at BL13W beamline at Shanghai synchrotron radiation facility (SSRF).

Solid-state electrochemical redox control of the optoelectronic properties for SrFeOx thin films

By utilizing redox reactions, the physical properties of several transition metal oxides can be drastically changed, which is useful for developing multifunctional memory devices. Strontium iron oxide (SrFeOx), which exhibits a clear phase transition from antiferromagnetic insulator (x = 2.5) to helimagnetic metal (x = 3), is a good candidate for the active material in multifunctional memory devices. However, practical applications using previous demonstrations of redox reactions in SrFeOx are limited by the use of a liquid electrolyte due to the leakage problem. Here, we demonstrate solid-state electrochemical redox reaction in SrFeOx using a yttria-stabilized zirconia (YSZ) single-crystal substrate as the solid electrolyte. We fabricated the SrFeO2.5 film on the YSZ substrate and the applied electric current using Au electrodes. The phase gradually changed from SrFeO2.5 to SrFeO2.5+x and SrFeO3−x. The color of the film changed from yellowish-transparent to dark brown. Although the as-grown SrFeO2.5 film showed high resistivity (ρ &amp;gt; 101 Ω cm), the ρ dramatically decreased (∼10−2 Ω cm) with increasing the applied charge density. Simultaneously, the thermopower greatly decreased from ∼+200 to ∼−10 μV K−1. The present results would provide a design concept for future SrFeOx-based solid-state multifunctional memory devices.

Additive Manufacturing for Rapid Prototyping of Mixed Potential Electrochemical Sensors

Natural gas pipeline leaks are responsible methane emissions that amount to over 1.6 x 108 metric tons of CO2 equivalent and more than 2 billion dollars in losses.[1, 2] A widely deployable sensor capable of remotely monitoring pipelines to promptly detect these leaks is needed to curb their environmental and economic impact. YSZ based mixed-potential electrochemical sensors (MPES) fit this need as they are cheap and durable, allowing for wide deployment in the field. Prototyping of these sensors is enhanced by the utilization of additive manufacturing (AM).The long lead times and high start-up cost of traditional ceramic manufacturing techniques are poorly suited to prototype development of mixed potential electrochemical sensors. Recent advances in AM techniques have opened the possibility for the rapid prototyping of these sensors.[3] We report for the first time a three element mixed potential electrochemical sensor manufactured using direct write syringe extrusion. La0.87Sr0.12CrO3 (LSCO), In2-xSnxO3 (ITO), Au and Pt electrodes bridged with a porous yttria-stabilized zirconia (YSZ) solid electrolyte have been deposited on YSZ substrates. The Pt electrode and leads, as well as the porous YSZ electrolyte and YSZ substrate are deposited by direct write extrusion. The printing parameters for the printing of the YSZ substrate are optimized to achieve desired surface and bulk material characteristics. A density 60% of theoretical of the YSZ substrate is obtained after sintering at 1450 C. The sensors are evaluated for their sensitivity to methane, ethane, ammonia, nitrous oxide, and hydrogen. The sensitivity of the sensors will be compared to that of an industry standard MidIR sensor for natural gas detection.[1] A.J. Marchese, T. L. Vaugh, D. J. Zimmerle, D. M. Martinez, L. L. Williams, A. L. Robinson, A. L. Mitchell, R. Subramanian, D. S. Tkacik, J. R. Roscioli, S. C. Herndon. Science. 7204 (2018).[2] Kort, E. A.; Frankenberg, C. Costigan, K.R.; Lindenmaier, R.; Dubey, M. K; Wunch, D. Geophys. Res. Lett, 2014, 41, 19, 6898[3] Travitzky, N., Bonet, A., Dermeik, B., Fey, T., Filbert‐Demut, I., Schlier, L., Schlordt, T. and Greil, P., 2014. Additive manufacturing of ceramic‐based materials. Advanced engineering materials, 16(6), pp.729-754.Figure 1. Additively manufactured three electrode pair mixed potential electrochemical sensor. Figure 1

Electrochemically controlled defect chemistry: From oxygen excess to deficiency

Fundamental understanding of materials properties requires the study and development of defect chemical reactions and models. In-depth analysis of the defect chemistry of metal oxides, however, has generally been limited to the oxygen deficient regime. Here, we present a defect chemical study covering both oxygen deficient and excess regimes using donor-doped layered cuprate (La1.85Ce0.15CuO4+δ) thin films over a wide range of oxygen activity levels. Unlike perovskite- or fluorite-structured oxides, layered cuprates can readily accommodate oxygen interstitials as well as vacancies. The scope of the defect chemical study was extended to include highly oxidizing conditions equivalent to many orders of magnitude higher oxygen activities than ambient pressure. This was achieved by electrochemical pumping of oxygen through an ionically conducting yttria-stabilized zirconia (YSZ) substrate with oxygen nonstoichiometry values derived from in situ chemical capacitance measurements between 500°C and 650°C. The defect chemical model was correlated with in-plane conductivity at different oxygen pumping levels in the temperature regime of 275~350°C. Thermodynamic parameters - thermal band gap, enthalpy of reduction and anion Frenkel-pair formation - were derived from a defect chemical analysis. The approach taken here can be extended to other layered oxides and opens up the possibility of accessing much broader oxygen activity limits and thereby an extended range of defect regimes and neighboring phases.

Durability of Colloidally Stabilized Supported Nickel and Nickel Platinum Nanoparticles during Redox-Cycling

We report on the oxidation and reduction behavior of colloidally stabilized Ni nanoparticles and Pt@NiPt core–shell nanoparticles with a platinum content of 4%. Thin films of both nanoparticle systems were deposited on yttria-stabilized zirconia substrates by spin-coating. Oxidation–reduction cycles were used to remove oxides and organics and obtain metallic particles. The cycling conditions necessary to clean and reduce Pt@NiPt core–shell nanoparticles were milder than for the Ni nanoparticles, which also needed several cycles to burn off residual organics. During cycling, the Ni nanoparticles lost their initially epitaxial relationship with the substrate and adopted a random orientation, while no epitaxial orientation was observable for the core–shell nanoparticles. Reasons for this are discussed together with the influence of platinum on Ni reduction. The Ni and Pt@NiPt nanoparticles sintered during the process but retained crystalline domain diameters close to the original particle diameters. Our results show that colloidally stabilized nanoparticles can be transferred onto a technologically relevant substrate and be reduced to metallic nanoparticles. The fabrication and final structures are discussed as a feasible route to realize solid oxide fuel cell anodes with tailored nickel particle diameter.

Epitaxial Ferroelectric Hf0.5 Zr0.5 O2 with Metallic Pyrochlore Oxide Electrodes.

The synthesis of fully epitaxial ferroelectric Hf0.5 Zr0.5 O2 (HZO) thin films through the use of a conducting pyrochlore oxide electrode that acts as a structural and chemical template is reported. Such pyrochlores, exemplified by Pb2 Ir2 O7 (PIO) and Bi2 Ru2 O7 (BRO), exhibit metallic conductivity with room-temperature resistivity of <1 mΩ cm and are closely lattice matched to yttria-stabilized zirconia substrates as well as the HZO layers grown on top of them. Evidence for epitaxy and domain formation is established with X-ray diffraction and scanning transmission electron microscopy, which show that the c-axis of the HZO film is normal to the substrate surface. The emergence of the non-polar-monoclinic phase from the polar-orthorhombic phase is observed when the HZO film thickness is ≥≈30nm. Thermodynamic analyses reveal the role of epitaxial strain and surface energy in stabilizing the polar phase as well as its coexistence with the non-polar-monoclinic phase as a function of film thickness.

Growth Parameter Based Control of Cation Disorder in MgSnN2 Thin Films

MgSnN $$_2$$ thin films have been grown on yttria-stabilized zirconia substrates via plasma-assisted molecular beam epitaxy and analyzed using reflection high-energy electron diffraction, X-ray diffraction, optical transmission, and cathodoluminescence. By systematically varying the growth parameters, particularly the substrate temperature, Mg:Sn flux ratio, substrate, and nitrogen flow rate, we were able to achieve high quality films and control disorder in the cation sublattice. This control of disorder allows for the ability to adjust the band gap continuously over a wide range of values.

Growth and characterization of pyrochlore-type (Ca,Ti)2(Nb,Ti)2O7 thin films

Pyrochlore-type (Ca,Ti)2(Nb,Ti)2O7 thin films have been grown on single-crystalline LaAlO3 and yttria-stabilized zirconia substrates by a magnetron sputtering system. Atomic-scale interface structure and growth mode of the (Ca,Ti)2(Nb,Ti)2O7 films on the substrates with different crystal structures have been investigated by advanced electron microscopy techniques. In both heterosystems, the film/substrate orientation relationship of [100](001)film//[100](001)substrate has been determined. In the heterosystem of (Ca,Ti)2(Nb,Ti)2O7/yttria-stabilized zirconia, the films directly grow on the substrates. In contrast, in the (Ca,Ti)2(Nb,Ti)2O7/LaAlO3 heterosystem, a perovskite-type Ca1-□(Ti,Nb)O3 interlayer with a few unit cells in thickness forms at the interface and interfacial reconstruction occurs at the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface. Our findings indicate that the formation of the interlayer and the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface reconstruction can accommodate the film/substrate dissimilarities in the crystal structures and facilitate the growth of single-crystalline pyrochlore-type films on the perovskite-type substrates.

Long-term stability of SOFC glass sealant under oxidising and reducing atmospheres

The behaviour of the 59.6SiO2–11.0Al2O3–6.6ZrO2–3.4CaO–15.4Na2O–4Y2O3 (wt. %) non-crystallising glass sealant was studied while in contact with NiO–YSZ (yttria-stabilized zirconia) ceramics and an Fe–Ni alloy after exposure to reducing and oxidising atmospheres at 850 °C and while on a Pt substrate. The sealant was completely amorphous after exposure on a Pt substrate for 1000 h in an air atmosphere. After exposure on a NiO–YSZ substrate in both oxidising and reducing atmospheres, no interaction on the NiO(Ni)–YSZ|sealant interface was observed. For the Fe–Ni alloy substrate, the formation of an Fe2SiO4 layer was observed after exposure in an oxidising atmosphere. In the reducing atmosphere, the Fe–Ni alloy substrate intensified sealant crystallisation, leading to the formation of numerous crystalline phases, but no interaction on the Fe–Ni alloy|sealant interface was observed.

Toluene-Sensing Properties of Solid-Electrolyte Gas Sensors Using CeO2-Added Au Thin-Film As Sensing Electrodes

Introduction The exhaled breath of patients contains higher concentrations of specific gases than those of healthy people. For example, the patients suffering from lung cancer, diabetes and periodontitis release high concentrations of toluene, acetone and methylmercaptan, respectively. Among various kinds of gas sensors, solid-electrolyte gas sensors have shown enhanced sensing properties to volatile organic compounds (VOCs) by optimizing the microstructure as well as composition of the sensing electrode (SE) [1]. We have also reported that the addition of CeO2 to the Au SE of yttria-stabilized zirconia (YSZ)-based gas sensors increased the toluene response [2, 3]. In this study, thin-film CeO2-added Au SEs (thickness: 30‒100 nm) were fabricated by a spin-coating method, and their sensing properties to toluene were examined at 500°C. Experimental CeO2-added Au SEs were fabricated by a spin-coating method. The coating solution was prepared by the addition of Ce(NO3)3ˑ6H2O and polyvinyl alcohol into a 0.1 M HAuCl4 aqueous solution. The solution was dropped on the YSZ substrate, and it was spun at 3000 rpm for 30 s, followed by the heat treatment at 300°C. This process was repeated multiple times to increase the film thickness. Then, they were annealed at 700°C for 2 h in air. The obtained SEs were denoted as nCeO2/Au(x) SEs (n: an additive amount of CeO2, 8‒24 (wt%), x: the number of spin-coating cycle, 5–15). A Pt paste was screen-printed on the backside of the YSZ as the counter electrode (CE), and it was annealed at 700°C for 2 h in air. Response properties of the fabricated sensors (nCeO2/Au(x) sensors) to 50 ppm toluene in dry air were measured in a flow apparatus (gas-flow rate: 100 cm3 min−1) at 500°C. The SE was exposed to a sample gas, while the CE was always exposed to dry synthetic air during gas response measurements. The open circuit voltage between the two electrodes (E, mV) of the sensors as a sensing signal was measured with a digital electrometer, and the response (ΔE) was defined as the difference in E between in dry air and in toluene balanced with dry air. The microstructure of the sensors was observed by scanning electron microscopy (SEM; JEOL Ltd., JSM-7500F). Results and Discussion The thickness of the 8CeO2/Au(5) SE was very thin (ca. 30 nm), and the thickness increased with the number of spin-coating cycles. The SE thickness was not affected by the additive amounts of CeO2 in the examined number of spin-coating cycles (x). Therefore, the SE thickness was controlled from 30 to 100 nm only by changing the x value.Figure 1 shows response transients of the nCeO2/Au(x) sensors to 50 ppm toluene at 500°C in dry air. The E values of all the sensors negatively shifted upon exposure to toluene, but ΔE was largely affected by the SE thickness and the additive amount of CeO2. ΔE of the 8CeO2/Au(x) sensors largely decreased with an increase in the thickness of SEs. Generally, the VOC-sensing mechanism of solid-electrolyte gas sensors can be explained on the basis of the mixed potential theory [1‒3]. Based on the theory, the electrochemical oxidation of toluene and electrochemical reduction of oxygen simultaneously proceed at triple phase boundaries (TPBs) at the interface between SE and YSZ, when toluene diffuses in SE and reaches TPBs [2]. In addition, a certain amount of toluene is catalytically oxidized during the diffusion in SE. Therefore, the actual concentration of toluene at TPBs decreased with an increase in the SE thickness, which resulted in the largest toluene response of the 8CeO2/Au(5) sensor among the 8CeO2/Au(x) sensors. However, ΔE of the 24CeO2/Au(x) sensors increased with an increase in the thickness of SEs, and the 24CeO2/Au(15) sensor showed the largest ΔE (ca. 199 mV) among the sensors examined. The details of this phenomena will be discussed in the presentation.

Magnetic Modulation by Oxygen Vacancies in Epitaxial Ga0.5Fe1.5O3−δ

Oxygen vacancies have often been believed to reduce ferroic properties. However, in this work, we demonstrated that oxygen vacancies caused enhanced magnetism in ferrimagnetic Ga0.5Fe1.5O3−δ by preventing Fe-O hybridization and formation of Fe2+. Epitaxial films of 001 Ga0.5Fe1.5O3−δ (GFO) were synthesized on (001) yttria-stabilized zirconia substrates by using radio-frequency magnetron sputtering, and the films were cooled in a forming gas. To see the effect of the oxygen content, we also prepared post-annealed GFO films in 500 Torr of O2. From the analyses of the structural and the optical properties, the magnetism, and the chemical state of the two prepared samples, we verified that oxygen vacancies induced lattice expansion, reduced p-d hybridization, and importantly enhanced magnetism, i.e., increased magnetic moments and the transition temperature. Our results reveal that the superexchange interaction governing the magnetism of GFO can be controlled by the oxygen vacancy content.

Ferroelectric properties of HfO2 nanodots with a diameter smaller than 10 nm deposited on an ITO bottom electrode

HfO2 nanodots and epitaxial HfO2 thin films with ferroelectric properties were grown on yttria-stabilized zirconia substrates with indium tin oxide bottom electrodes via a pulsed laser deposition (PLD) method. The crystallinity and ferroelectric properties of the epitaxial HfO2 thin films were analyzed to compare ferroelectric properties resulting from crystallinity and the strained structure of HfO2 nanodots. Using the total number of PLD pulses as a control, it was possible to grow HfO2 nanodots with diameters of 7, 12, and 20 nm and heights of 4.9, 7.8, and 14.8 nm. Based on the d33 piezoelectric hysteresis loops and polarization switching phenomena, it was confirmed that the HfO2 nanodots exhibited good ferroelectric properties even for scaling of less than 7 nm in diameter. The observation of the piezoelectric d33 hysteresis loop of the HfO2 nanodots and epitaxial HfO2 thin films revealed that HfO2 nanodots had improved ferroelectric properties due to the size effect.