Fabrication and characterization of bioactive zirconia-based nanocrystalline glass-ceramics for dental abutment

Zirconia-based ceramics are becoming a popular biomaterial in dental implantology due to their natural silver-white color, excellent mechanical properties, and good biocompatibility. However, zirconia-based ceramics are biologically inert, which limits their ability to integrate with the surrounding human tissues. To solve this problem, the bioactive elements of calcium (Ca) and phosphorus (P) were doped in high-strength ZrO₂–SiO₂ nanocrystalline glass-ceramics (NCGCs) to overcome the biological inertness of ZrO₂-based ceramics. XRD results showed that tetragonal zirconia (t-ZrO₂) and monoclinic zirconia (m-ZrO₂) were the only two crystalline phases after spark plasma sintering. Ca and P dopants acted as destabilizer of t-ZrO₂, enhancing its transformability to m-ZrO₂ during sintering. The amount of t-ZrO₂ exerted significant effects on the average flexural strength of the NCGCs. The NCGC with 45 mol% ZrO₂ were composed of 64.5 vol% t-ZrO₂ and 35.5 vol% m-ZrO₂ after sintering at 1230 °C. And, the average flexural strength and Vickers hardness of the NCGC was 615 MPa and 1049 HV, respectively. In comparison, the NCGC with 65 mol% ZrO₂ were composed of 12.6 vol% t-ZrO₂ and 87.4 vol% m-ZrO₂ after sintering at 1150 °C. The average flexural strength and Vickers hardness of the NCGC was 293 MPa and 839 HV, respectively. Interestingly, the NCGCs exhibited a plastic deformation behavior during flexural strength test, which was different from traditional brittle ceramics. The ion release results demonstrated that Ca²⁺ and Si⁴⁺ ions kept on releasing from the surface of the material. The formation of hydroxyapatite in the in-vitro apatite formation test indicated that the NCGCs had good biological activity. The doped ZrO₂-based NCGCs combined moderate strength and good bioactivity. Hence, the NCGCs show promising potential to be used in sub-gingival regions, such as dental abutments.     

Combining good mechanical properties and high translucency in yttrium-doped ZrO2-SiO2 nanocrystalline glass-ceramics

It is challenging to develop a material that combines good mechanical properties and high translucency since these properties are generally not coincident in one material. In this study, we prepared ZrO₂-SiO₂ nanocrystalline glass-ceramics that combines the above two types of properties. Raw powder with 55 mol%, 65 mol%, and 75 mol% ZrO₂ and each with 5 mol% yttrium as a dopant was prepared by sol-gel method, followed by spark plasma sintering to obtain dense glass-ceramics. XRD results demonstrated that the glass-ceramics with 65 mol% and 75 mol% ZrO₂ were composed of tetragonal-ZrO₂, whereas, that with 55 mol% ZrO₂ was composed of cubic-ZrO₂. The as-sintered glass-ceramics showed black/brown discoloration, but they obtained high translucency after thermal treatment. X-ray energy-dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated yttrium dopants were predominately distributed in ZrO₂ nanocrystallites. The glass-ceramics with 65 mol% ZrO₂ had the highest flexural strength, achieving an average value of 673 MPa. The glass-ceramics with different compositions sintered at different temperatures showed fracture toughness values ranging from 5.25 MPa m^1/2 to 6.69 MPa m^1/2. The strong and translucent ZrO₂-SiO₂ nanocrystalline glass-ceramics showing great protentional to be used in many fields.     

Bioceramics and their application for dental restoration

Abstract

This review article covers the historical development of ceramics, from the beginnings to the present. Feldspar based ceramic biomaterials for veneering metal frameworks, which are based on the jacket porcelain crown, have firmly established themselves in restorative dentistry since the 1970s. Currently, the development of restorative dental materials that can be used to replace metal represents a major challenge. As a result, this review will focus on the latest materials in this field. These materials include glass ceramics as well as high performance sintered ceramics. Glass ceramics exhibit more favourable optical properties, such as translucency and colour, compared with high performance ceramics, while the latter demonstrate high flexural strength and toughness. Both groups of materials have specialised applications in restorative dentistry and are capable of covering all the indications of dental restorations. The two types of materials, that is, glass ceramics and ceramics, have to be processed in accordance with their properties. As a result, the processing techniques, such as moulding, sintering and machining, will be discussed in detail in addition to the properties of the materials. Additional development possibilities for the materials will be presented on the basis of customer/patient needs and the successful long term use of glass ceramics and ceramics. In this context, it is clear that high performance ceramics and layered composites (consisting of high performance ceramics veneered with glass ceramics) offer the best possible solution for indications in the posterior region of the mouth. In contrast, glass ceramics are used to fabricate inlays and onlays for all parts of the jaw. In addition, glass ceramics can be used to fabricate crowns and small bridges to replace anterior dentition.     

Li2ZrO3 based Li-ion conductors doped with halide ions & sintered in oxygen-deficient atmosphere

All-solid-state batteries have recently attracted much attention for their high energy density and safety. Li₂ZrO₃-based Li-ion conductors with high electrochemical stability have potential applications for electrolytes in all-solid-state batteries. In this work, comparative investigations of Li₂ZrO₃ and halogen doped Li₂ZrO₃ ceramics were conducted by sintering at 700 °C in air or in oxygen-deficient atmosphere which was induced by a simple setup covering with corundum crucible. The analysis of phase composition reveals that the undoped Li₂ZrO₃ ceramic sintered in air contains pure monoclinic phase, while halogen-doped Li₂ZrO₃ sintered in air and all ceramics sintered in oxygen-deficient atmosphere are simultaneously composed of monoclinic and tetragonal phases. Li₂ZrO₃ ceramic with tetragonal phases has higher conductivity (0.28 mS cm⁻¹ for undoped Li₂ZrO₃) than the pure monoclinic Li₂ZrO₃ (0.07 mS cm⁻¹), and halogen doping can further enhance the conductivity of Li₂ZrO₃ ceramics higher than 0.5 mS cm⁻¹ at room temperature.     

Observation of yttrium oxide segregation in a ZrO2-SiO2 glass-ceramic at nanometer dimensions

Dopant segregation at grain boundaries (GBs) in ceramics has been widely reported, while whether similar segregation behavior occurs in glass-ceramics remains unknown. The distribution of dopant in glass-ceramics may be totally different due to the existence of glass phase. This study examines the distribution of Y³⁺ ions in a ZrO₂-SiO₂ glass-ceramic. Two samples were prepared by hot pressing, yttrium oxide-doped, and undoped 65 mol% ZrO₂-35 mol% SiO₂ nanocrystalline glass-ceramics (NCGCs). The NCGCs had the same microstructure, that is, ZrO₂ nanoparticles (NPs) embedded in an amorphous SiO₂ matrix. XRD results showed that the undoped NCGC was composed of 20.9 wt% (weight percentage) monoclinic ZrO₂ (m-ZrO₂) and 79.1 wt% tetragonal ZrO₂ (t-ZrO₂), while the yttrium oxide-doped NCGC was composed of 9.6 wt% m-ZrO₂ and 90.4 wt% t-ZrO₂. X-ray energy-dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated that Y³⁺ ions segregated both on the surface of ZrO₂ NPs and within the thin intergranular glass film (with a thickness of approximately 7 Å) between ZrO₂ NPs in the yttrium oxide-doped NCGC. Interestingly, no obvious Y signals were detected in the amorphous SiO₂ matrix. Density functional theory calculation results showed that Y³⁺ ions had a strong segregation tendency in the GB area and the segregation of Y³⁺ ions increased the work of separation of GB layer. These findings provide new understanding of the segregation behavior of dopant in glass-ceramics, which may offer useful guidance for other researchers to tailor the properties of glass-ceramics through GB engineering.     

Terahertz probing of low-temperature degradation in zirconia bioceramics

ZrO₂-based ceramics are widely used in biomedical applications due to its color, biocompatibility, and excellent mechanical properties. However, low-temperature degradation (LTD) introduces a potential risk for long-term reliability of these materials. The development of innovative nondestructive techniques, which can explore LTD in zirconia-derived compounds, is strongly required. Yttria stabilized zirconia, 3Y-TZP, is one of the well-developed ZrO₂-based ceramics with improved resistance to LTD for dental crown and implant applications. Here, 3Y-TZP ceramic powders were pressed and sintered to study the LTD phenomenon by phase transition behavior. The LTD-driven tetragonal-to-monoclinic phase transition was confirmed by XRD. XPS analysis demonstrated that induced LTD reduced the oxygen vacancies which supports these findings. It is proved that after the degradation, the 3Y-TZP ceramics show the decreased dielectric permittivity at terahertz frequencies due to the crystallographic phase transformation. Terahertz nondestructive probe is a promising method to investigate LTD in zirconia ceramics.     

Thermal and mechanical behavior of ZrTiO4-TiO2 porous ceramics by direct foaming

This paper reports the production of micro porous ceramics consisting of TiO₂ and ZrO₂ by direct foaming. ZrO₂ particles in a colloidal suspension were partially hydrophobized using propyl gallate as an amphiphile at a suitable pH range of around 3.5–4.5. A TiO₂ suspension with different mole ratios was added to the surface modified ZrO₂ suspension to obtain ZrTiO₄-TiO₂ porous ceramics in the sintered sample. The influence of the TiO₂ content and calcination temperature on the phase transformation, microstructure, and thermal properties of the materials was determined by thermal analysis, X-ray diffraction, field emission scanning electron microscopy, and dilatometry. The crystallization of ZrTiO₄ (orthorhombic) was observed at 1100 °C on the thermal hysteresis curve due to anisotropic thermal expansion. The compressive load and displacement of the sintered porous ceramics samples were calculated using the Hertzian indentation method.     

Highly translucent and strong ZrO2-SiO2 nanocrystalline glass ceramic prepared by sol-gel method and spark plasma sintering with fine 3D microstructure for dental restoration

Balance of better mechanical strength and good translucency for dental restorative materials is always a challenge. A translucent glass ceramic/ceramic with improved mechanical properties or a strong glass ceramic/ceramic with good translucency would therefore be interesting for dental application. Nanocrystalline glass ceramics (NCGC) attract a lot attention because of their superior optical and mechanical properties. This study aims to obtain ZrO₂-SiO₂ nanocrystalline glass-ceramic that possesses high mechanical strength as well as excellent translucency by controlling the content, size, and connection of nanocrystalline ZrO₂ in a ZrO₂-SiO₂ glass-ceramic material. Toward this end, well-homogenized nano-powders with three different compositions, 45%ZrO₂-55%SiO₂ (molar ratio, 45Zr), 55%ZrO₂-45%SiO₂ (55Zr), and 65%ZrO₂-35%SiO₂ (65Zr)_, were synthesized, followed by a fast sintering process. Highly-translucent nanocrystalline glass ceramics composed of tetragonal ZrO₂ were obtained. Samples with high zirconia content showed that the structure of the skeleton was predominately built by nano-sized ellipsoidal ZrO₂ particles bonded by grain boundaries, with amorphous SiO₂ filling the voids between the ZrO₂ particles. The achieved flexural strength measured by piston-on-three-ball test was as high as 1014 MPa. To our knowledge, this is one of the highest flexural strength values of glass ceramics ever reported, which is higher than transparent zirconia and alumina ceramics. The 3D structure of nanocrystalline zirconia in silica matrix did enhance the flexural strength of the NCGC. The results of this study suggest that the new ZrO₂-SiO₂ NCGC has great potential of using as dental restoration.     

Enhancement of piezoelectric properties of BF–BT ceramics by using ZrO2 powder bed during the sintering process

ZrO₂ powders of various particle sizes (0.15, 0.7, 500 µm) were used to simulate loose powder bed sintering to prepare BF–BT piezoelectric ceramics. The phase structure, dielectric properties, ferroelectric properties, and piezoelectric properties were compared with the samples sintered by the conventional powder bed method (i.e., powder of the same composition as the sample). Results showed that the use of loose ZrO₂ powder bed could improve the heat conduction rate and the sintering quality of bulk BF–BT piezoelectric ceramics. The XPS results showed that the samples sintered with 500 µm ZrO₂ powder beds had the lowest concentration of Fe²⁺, exhibited the largest piezoelectric coefficients (d₃₃ = 201 pC/N). In contrast, the sample sintered with a conventional powder bed under the same sintering conditions had a piezoelectric coefficient d₃₃ of 156 pC/N.     

Effect of Fe2O3 doping on color and mechanical properties of dental 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, iron(III) oxide (Fe₂O₃)-doped zirconia (3Y-TZP) ceramics with desirable mechanical and color properties for dental restorations were fabricated by stereolithography-based additive manufacturing. Six zirconia ceramic paste specimens with high solid loading (58 vol%) and reasonably low viscosity were prepared according to doped content of Fe₂O₃ (0–0.14 wt%). Zirconia ceramics were fabricated using commercial stereolithography three-dimensional printer and sintered at 1500 °C for 4 h to obtain final dense parts with a relative density of above 99%. Effects of Fe₂O₃ doping on microstructure, mechanical properties, and color of 3Y-TZP ceramics were investigated. Results indicate that Fe₂O₃ exhibited little effect on the shrinkage and density of colored ceramics compared to uncolored ceramics. Average grain size of 3Y-TZP ceramics sintered at 1500 °C increased with increasing content of Fe₂O₃. X-ray diffraction analysis showed that tetragonal phase was dominant phase structure of white and colored 3Y-TZP ceramics, and monoclinic phase increased with increasing Fe₂O₃ content. Compared to uncolored specimens, Fe₂O₃ exhibited negative effects on three-point flexural strength (mean > 879.70 MPa), Vickers hardness (mean > 12.14 GPa), and indentation fracture toughness (mean > 4.23 MPa m^1/2) of the colored specimens. With the increase in the content of Fe₂O₃ from 0 to 0.14 wt%, L* (black–white index) value decreased from 83.39 to 79.54, a* (green–red index) value increased from −2.28 to −0.74, and b* (blue–yellow index) value increased from 1.15 to 17.94. Chromaticity (L*, a*, b*) fell within the range of natural tooth color, indicating that it is suitable for dental application because of its color compatibility with natural teeth. In addition, the transmittance slightly decreased with increasing Fe₂O₃ content. Thus, Fe₂O₃-doped 3Y-TZP ceramics can be used as potential candidates for aesthetic dental restoration materials.     

Preparation of glass-ceramics with low density and high strength using blast furnace slag,glass fiber and water glass

To reduce the production costs of glass-ceramics and broaden the application field of solid waste in steel industry, low-density and high-strength glass-ceramics were produced by using blast furnace slag as the basic material, choosing glass fiber and water glass as the strengthening agents. The effects of glass fiber and water glass on the phase composition, microstructure, apparent density, water absorption and compressive strength of glass–ceramics were investigated. The results show that the rod structure of glass fiber can be retained in the sintered samples and high content of diopside and augite significantly improve the compressive strength of glass-ceramics. Tiny spherical crystalline phases can be obtained for the glass-ceramics soaked in the moderate concentration of water glass. The BGW-2 samples fabricated with 70% blast furnace slag, 30% glass fiber and 4% water glass, exhibit excellent comprehensive properties. The bulk density, water absorption and compressive strength of BGW-2 are 1.76 g/cm³, 2.26% and 68 MPa, respectively. Consequently, using blast furnace slag to prepare glass-ceramics can be another applicable way to utilize blast furnace slag efficiently.     

Finely disperse powders of stabilized zirconia with flake particles

The possibility of using carbonic acid for the plasma chemical method of preparing finely disperse ZrO₂ powders with flake particles is investigated. The optimum parameters of the technological process and the basic properties of stabilized ZrO₂ recommended for the production of high-strength ceramics are determined.Translated from Steklo i Keramika, No. 12, pp. 12–14, December, 1995.     

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li₂O-Al₂O₃-SiO₂ (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li₂O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li₂O content. The effect of Li₂O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO₂ and ZrO₂ were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li₂O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li₂O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li₂O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li₂O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.     

Binder jetting yttria stabilised zirconia ceramic with inorganic colloid as a binder

ABSTRACT

The new inorganic colloid is a particle-free decomposable binder that can solve the nozzle clogging problem and precipitate zirconia particle upon heating. The inorganic colloidal binder can be used as a binder precursor to replace commonly used PVP binder in printing ZrO₂ ceramics parts using binder-jet technology. Green bodies were printed using inorganic colloid binders with different saturation level and PVP binder separately, then cured and sintered. The effects of binder saturation level and sintered temperature on the properties of the green and sintered bodies were investigated. After being deposited into the powder bed interstices and cured, the inorganic colloidal binder containing zirconium basic carbonate decomposes and forms ZrO₂ ceramic particles that are filled the interstices and sintered to provide bonding strength to the printed parts. Samples with inorganic colloidal binder eventually perform better surface quality and denser sintered body than polymer binder when using same saturation ratio.     

Microstructure of rapidly-quenched ZrO2-SiO2 glass-ceramics fabricated by container-less aerodynamic levitation technology

In this work, an aerodynamic levitation technology (ALT) was utilized to prepare ZrO₂-SiO₂ glass-ceramics with two different ZrO₂ contents, that is, 35 mol% and 50 mol%. The glass-ceramics were partially melted at ∼2000°C or fully melted at ∼3000°C by ALT, followed by rapid quenching to obtain spherical glass-ceramic beads. The phase compositions and microstructures of the glass-ceramics were characterized. Crystallization of ZrO₂ occurred during the solidification process and ZrO₂ content, processing temperature, and the addition of yttrium (3 mol%) affected the crystalline phase of ZrO₂. No ZrSiO₄ or crystalline SiO₂ were formed during the solidification process and the glass-ceramics were away from thermodynamic equilibrium due to rapid quenching. The glass-ceramics showed a microstructure of irregular-shaped ZrO₂ micro-aggregates embedded in an amorphous SiO₂ matrix, with lamellar twins and lattice defects formed within ZrO₂ crystals. For samples prepared at ∼3000°C, a liquid-liquid phase separation occurred in the melt, which eventually resulted in the formation of large and irregular-shaped ZrO₂ aggregates. In comparison, for samples prepared at ∼2000°C, pre-existed ZrO₂ crystals formed during heating acted as nucleation sites during the cooling process, followed by grain growth to form large ZrO₂ aggregates. Solidification and microstructure formation mechanisms were proposed to elucidate the solidification process during rapid cooling and the microstructure of the glass-ceramics obtained.     

Effect of titanium oxide addition on sintering performance of magnesia-rich magnesia-zirconia ceramics

MgO-ZrO₂ ceramics were prepared using MgO powder calcined with crystal magnesite as starting material and TiO₂ as an additive. Samples were mixed with different mass fractions of ZrO₂ powder and sintered at 1600 °C for 2 h. Effects of added amounts of ZrO₂ and TiO₂ on the performance of MgO–ZrO₂ ceramics were investigated. Results showed that increase in mass fraction of added ZrO₂ or addition of small amount of TiO₂ significantly promoted performance of MgO–ZrO₂ ceramics. Moreover, the improvement effect of TiO₂ was more obvious than that of ZrO₂. Addition of TiO₂ promoted solid solution reaction of ZrO₂ and MgO, which was the main reason for improved densification. In addition, TiO₂ and CaO form CaTiO₃, whereas free SiO₂ and MgO form Mg₂SiO₄. These two compounds filled the pores between MgO and ZrO₂ grains and improved densification, compressive strength, and thermal shock resistance.     

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li₂O–Al₂O₃–SiO₂ (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO₂ by SnO₂ on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO₂–SnO₂ increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO₂–SnO₂ was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.     

Sintering behavior and properties of lithium stabilized sodium β'' - alumina ceramics with YSZ addition

In this study, investigations of sintering behavior and properties were performed on lithium-stabilized Na-β''-alumina (LiSBA) ceramics with and without 15?wt% 8?mol% Y₂O₃ stabilized ZrO₂ (8YSZ) addition synthesized by solid phase reaction. Changes of phase composition, relative density, and grain size in the ceramics sintered at different temperature were analyzed. It was shown that phase transformation in sintering ceramics was controlled by relationship between the Na₂O evaporation and Li⁺ ions stabilization, while microstructure evolution was controlled by pore-boundary interaction. LiSBA with YSZ addition (Zr-LiSBA) showed more significant variation of β'' phase fractions, slower grain growth and faster densification with increasing sintering temperature, which were caused by enhanced Na₂O evaporation and gas transport by oxygen ion conductor ZrO₂ as well as the drag effect by second phase particles of YSZ in Zr-LiSBA ceramics. Zr-LiSBA specimens sintered at optimized condition achieved higher Vickers microhardness and intermediate Na⁺ ion conductivity.     

Fabrication of highly bioactive zirconia ceramics via grain-boundary activation for dental implants

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics with outstanding mechanical properties and aesthetic origins are expected to be used in dental implant applications. However, tetragonal zirconia ceramics are not bioactive, which affect the osseointegration and reliability as dental implant materials. Herein, in this study, Y-TZP ceramics were modified by grain-boundary activation via coating a bioactive glass (BG) sol with different content on the crystal surfaces of zirconia powder and followed by being gelled, dried, granulated, low-temperature treated, molded and sintered at 1450°C for 3 h in air. The effects of BG content on the morphology, phase compositions, mechanical properties, in vitro mineralization ability and cell biological properties of the bioactivity modified Y-TZP ceramics were evaluated. The BG additive did not affect the tetragonal–monoclinic phase transformation of ZrO₂. However, the addition of BG decreased the flexural strength of the modified Y-TZP ceramics compared to that of Y-TZP. The in vitro mineralization results showed that a homogeneous apatite layer was produced on the surface of the Y-TZP ceramics when they were immersed in the simulated body fluid for 21 days. The cell response results indicated that the bioactive surface modification of Y-TZP ceramics could promote cell adhesion, propagation and osteogenic differentiation performance. Thus, our research results suggest that the highly bioactive Y-TZP ceramics could be a potential candidate for dental implant material.     

ZrO2-doped Y2O3 transparent ceramics via slip casting and vacuum sintering

Commercial Y₂O₃ powder was used to fabricate highly transparent Y₂O₃ ceramics with the addition of ZrO₂ via slip casting and vacuum sintering. The effects of ZrO₂ addition on the transparency, grain size and lattice parameter of Y₂O₃ ceramics were studied. With addition of ZrO₂ the transparency of Y₂O₃ ceramics increased markedly and the grain size of Y₂O₃ ceramics decreased markedly by cation diffusivity mechanism and the lattice parameter of Y₂O₃ ceramics slightly decreased. The highest transmittance (at wavelength 1100 nm) of the 5.0 mol% ZrO₂–Y₂O₃ ceramic (1.0 mm thick) sintered at 1860 °C for 8 h reached 81.7%, very close to the theoretical value of Y₂O₃.