Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Materials development and potential applications of transparent ceramics: A review

Advanced ceramic components: Materials, fabrication, and applications

We report a double-ceramic-layer (DCL) thermal barrier coating (TBC) with high-entropy rare-earth zirconate (HE-REZ) as the top layer and yttria stabilized zirconia (YSZ) as the inner layer sprayed on Ni-based superalloy by atmospheric plasma spraying. La2Zr2O7 (LZ) was selected as a reference for the HE-REZ. Thermal cycling test results demonstrate that the HE-REZ/YSZ DCL coating exhibited obviously improved thermal stability when compared to the LZ/YSZ DCL coating. The reasons for the improvement of the thermal shock resistance are considered to be the anti-sinterability of the HE-REZ ceramics during the thermal cycling test attributed to the sluggish diffusion effect and as well as the better match in the coefficient of thermal expansion of HE-REZ coating with the YSZ inner layer. In addition, the HE-REZ coating maintains fluorite structure after thermal cycling test. This study makes one step forward in the development and application of high-entropy rare-earth zirconate ceramic thermal barrier coatings.

High-Entropy Thermal Barrier Coating of Rare-Earth Zirconate: A Case Study on (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 Prepared by Atmospheric Plasma Spraying

A novel one-pot biosynthesis of pure alpha aluminum oxide nanoparticles using the macroalgae Sargassum ilicifolium: A green marine approach

Gd2Zr2O7 nanoceramics were fabricated using pressureless sintering method, in which the nanopowders were synthesized via solvothermal approach. The effects of starting powders on grain growth and densification during sintering of ceramics were revealed. Two distinct pressureless sintering methods were investigated, including conventional and two-step sintering. The sample grain size increases abruptly as sintering temperature increases during conventional sintering. In contrast, in two-step sintering, abnormal or discontinuous grain growth was suppressed in the second step, leading to Gd2Zr2O7 nanoceramics formation (average grain size 83 nm, relative density ∼93%). Such distinct behaviors may originate from the interplay between kinetic factors such as grain boundary migration and diffusion. Moreover, suppression of grain growth and promotion of densification in the two-step sintering are mainly due to dominant role of grain boundary diffusion during the second-step sintering process.

Densification and grain growth of Gd2Zr2O7 nanoceramics during pressureless sintering

Fluorite (F)–pyrochlore (P)–fluorite (F) phase transitions of Gd2Zr2O7 were investigated from 573 K to 1873 K (300 °C to 1600 °C), by means of X-ray diffraction, infrared spectra (IR), and Raman spectra. The low-temperature F phase can stably exist below 1523 K (1250 °C) and the F–P transition occurs at 1523 K to 1573 K (1250 °C to 1300 °C). The ordering process of P phase forms at 1573 K to 1773 K (1300 °C to 1500 °C) and the ordering degree increases with increasing sintering temperature and heat preservation period. High-temperature phase transition from P to F occurs between 1773 K and 1823 K (1300 °C and 1550 °C). IR spectra of samples with different ordering degrees show an interesting shift at 510 cm−1. Raman spectra show that only the A1g
 mode displays a significant change between F and P phases. This ordering degree and phase transition temperature studies would allow a more targeted experimental optimization of Gd2Zr2O7 to use in nuclear waste host, thermal barrier coatings, and solid oxide fuel cells.

Thermal-Driven Fluorite–Pyrochlore–Fluorite Phase Transitions of Gd2Zr2O7 Ceramics Probed in Large Range of Sintering Temperature

A new and highly active sintering additive: SiO2 for highly-transparent AlON ceramic

Yttrium-stabilized zirconia (Y0.08Zr0.92O1.96, YSZ) nanocrystalline powders were prepared by co-precipitation methods. Different precipitants (ammonium hydroxide, ammonium bicarbonate, oxalic acid, and urea) were used to study the effects of precipitants on co-precipitation synthesis of YSZ nanocrystalline powders. Thermogravimetric analysis-differential scanning calorimetry, powder X-ray diffraction, Fourier-transform infrared, scanning electron microscope, energy-dispersive spectrometer, Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and X-ray photoelectron spectroscopy analysis methods were employed to investigate the thermal decompositions, phase evolutions, micro-morphologies, surface areas, and elements analysis of the synthesized YSZ precursor powders or nanoparticles. Although different precipitants were used, the calcined products at 600 °C have nearly identical chemical compositions. The crystallization temperature of the precursor powders to evolve to cubic phase is the lowest (about 400 °C) when ammonium hydroxide is used as a precipitant, while it is about 500 °C in the case of other three types of precipitants (ammonium bicarbonate, oxalic acid, and urea) that were used. Ammonium bicarbonate cannot precipitate ZrO2+ effectively in the solution, resulting in the formation of cubic Y0.18Zr0.82O1.91 at 1000 °C. Despite the time-consuming co-precipitation process, urea was proved to be the optimal precipitant in terms of the fabrication of nanocrystalline YSZ powders with designed Y/Zr/O molar ratio, large surface area, small crystallite size, and well dispersion.

The effects of precipitants on co-precipitation synthesis of yttria-stabilized zirconia nanocrystalline powders

Non-aqueous tape-casting forming technology was used in the fabrication of highly-transparent aluminum oxynitride (AlON) ceramics with different sizes and shapes. The tape-casting process utilizes the warm-pressing and the cold isostatic pressing methods, which can optimize the microstructure and increase the density of the AlON green tapes. In this work, highly-transparent AlON ceramics were fabricated by the pressureless sintering method at 1880 °C for 8 h. The transmittance of final polished AlON ceramic reaches 84 % at the wavelength of 2000 nm.

Zhao Feng

Papers

Thermal-Driven Fluorite–Pyrochlore–Fluorite Phase Transitions of Gd2Zr2O7 Ceramics Probed in Large Range of Sintering Temperature

Densification and grain growth of Gd2Zr2O7 nanoceramics during pressureless sintering

A new and highly active sintering additive: SiO2 for highly-transparent AlON ceramic

The effects of precipitants on co-precipitation synthesis of yttria-stabilized zirconia nanocrystalline powders

Highly-transparent AlON ceramic fabricated by tape-casting and pressureless sintering method