Properties Of Pyrochlores Research Articles

The Structure, Property, and Ion Irradiation Effects of Pyrochlores: A Comprehensive Review

Since the beginning of the use of nuclear energy, humans have been faced with the problem of radionuclide disposal. At present, a large amount of waste is stored in pools or dry tanks at reactor sites. With the development of the nuclear power generation industry worldwide, the high storage cost (including building, maintaining, and operating storage pools) is overwhelming and serious, and urgent radionuclide disposal problems have become increasingly difficult. Safe and economical strategies are urgently needed for long-term storage and disposal of nuclear waste, which has become among the core issues in the utilization of nuclear energy. Pyrochlore ceramics are able to immobilize a variety of radionuclides and have excellent irradiation stability, so they have received extensive attention as hosts of radionuclides waste. This review summarizes the structure, composition, synthesis process, properties, and irradiation stability of pyrochlore ceramics, focusing on the ion irradiation effect of pyrochlore. In general, the cation radii ratio rA/rB is a key parameter related to various properties of pyrochlores. Zirconate pyrochlore is more easily transformed from pyrochlore to defective fluorite, and leads to better irradiation resistance.

Tailoring magnetic and dielectric properties of Yb2Ti2O7 pyrochlore through structural distortion

While the unique geometrical frustration of pyrochlore Yb2Ti2O7 has attracted attention, the dielectric and other properties of this pyrochlore beyond frustrated magnetism are not well understood. Here, we report on the fascinating low-temperature dielectric relaxation of Yb2-xBaxTi2O7-δ (x = 0–0.20) and demonstrate that this phenomenon is related to structural distortion. A-site Ba substitution, which increases the density of point defects and introduces a different atomic radius, enhances the chemical disorder and structural distortion. As a result, the increases in oxygen vacancies and nonmagnetic Ba2+ and Yb2+ ions dilute the ferromagnetic Yb3+–Yb3+ interactions, as indicated by the decrease in effective magnetic moment. On the other hand, the distorted octahedra facilitate the hopping of Yb ions, and the random distribution of Ba2+ ions at the Yb3+ sites gives rise to additional random fields, leading to significantly increased dielectric relaxation. The room-temperature dielectric constant is improved to ∼170, twice that of pristine Yb2Ti2O7. This work provides a comprehensive view of the structural, magnetic, and dielectric properties of Yb2Ti2O7 and lays the foundation for additional research into pyrochlore compounds.

Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials, Processes, and Properties

The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined.

Phase Relation and Dielectric Properties of Bi 2 O 3 -ZnO-Nb 2 O 5 -Based Ceramics

The crystal structure and dielectric properties of pyrochlore (a=10.5 A) Bi 1.65 (Zn 2/3 Nb 4/3 )O 6.5 ceramics and a new compositional ceramic Bi(Zn 2/3 Nb 1/3 )O 3 having disordered-fluorite type structure have been studied. The samples are prepared in the sintering temperature range 850∼1100°C depending on the substitution atoms. The pyrochlore structure is Fd-3m(a=10.5 A) and the new disordered fluorite type structure can be described by Fm-3m or F-43m(a=5.45 A). By the Nd, La, and Y substitutions in the pyrochlore phase, the temperature coefficient of dielectric permittivity ‰ l can be stabilized to near zero value. Loss tan i and l r change in the range of 0.0001∼0.0025 and 67∼87 respectively.

Phase Relation and Dielectric Properties of Bi 2 O 3 -ZnO-Nb 2 O 5 -Based Ceramics

The crystal structure and dielectric properties of pyrochlore (a=10.5 Å) Bi 1.65 (Zn 2/3 Nb 4/3 )O 6.5 ceramics and a new compositional ceramic Bi(Zn 2/3 Nb 1/3 )O 3 having disordered-fluorite type structure have been studied. The samples are prepared in the sintering temperature range 850∼1100°C depending on the substitution atoms. The pyrochlore structure is Fd-3m(a=10.5 Å) and the new disordered fluorite type structure can be described by Fm-3m or F-43m(a=5.45 Å). By the Nd, La, and Y substitutions in the pyrochlore phase, the temperature coefficient of dielectric permittivity l can be stabilized to near zero value. Loss tan i and l r change in the range of 0.0001∼0.0025 and 67∼87 respectively.