No abstract

The structural properties of Bi0.75Pr0.25O1.5 have been investigated by powder X-ray and neutron diffraction as a function of temperature up to around 800 °C. A layered rhombohedral structure is confirmed throughout the temperature range studied, with an orderdisorder type phase transition (β2 ↔ β1) at ca. 730 °C. This transition is accompanied by partial migration of the oxide ions from the fluorite-like blocks of the layered structure to interstitial sites in the van der Waals gap between blocks. A reversible step change in total conductivity, associated with the phase transition, is preceded by non-linear behaviour observed in the Arrhenius plot of total conductivity at lower temperatures. A theoretical model based on a modification of the "cube-root" model successfully describes the conductivity data through the phase transition, showing the transition to involve a jump in inter-planar conductivity correlated with the appearance of interstitial oxide ions in the van der Waals gap. While the "cube root" model has been successfully used to explain phase transitions in classic 3-dimensional ionic conductors, the present study represents the first example of application of this model to a lower dimensional system.

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.

Three kinds of commercial zirconia powders with compositions (1-x)ZrO 2 -xY 2 O 3 (x = 0, 3 and 8 mol-%) were sintered at 1300-1600°C in their free-standing granules. The as-received powder with x = 0 is monoclinic (M) phase. Both as-received powders with x = 3 and 8 show mixed phases dominated by tetragonal (T). The powder with x = 0 returned to M phase at room temperature after high temperature sintering. The powder with x = 3 transfer from mixed phase (T + M) to single phase T after sintering at 1300°C or 1400°C. Moreover, minor M phase appears again when the sintering temperature is above 1400°C, sintering the powder with x = 8 shows only T phase after sintering at different temperatures.

The temperature dependence of ageing in the commercial zirconia ceramic is crucial in the applications of dental implants. This study investigated the relationship between structure and mechanical properties of the zirconia dental ceramics and their susceptibility to human body temperature in a prolonged time. Commercial samples were put into exaggerated low-temperature degradation (LTD) as per ISO standard and three-quarters of its ageing temperature to see its effect on LTD in zirconia-based ceramics. The results reveal a negligible effect of LTD on the material at a temperature lower than 134°C, which is the standard LTD temperature for zirconia.

No abstract

Yttria-stabilised zirconia (Y-TZP) ceramics are widely used for dental and prosthesis applications; however, they are susceptible to low-temperature degradation (LTD). Despite several explanations of the LTD mechanism, it is not fully understood yet. Commercial TZ-3Y-E grade powder was used to further study the LTD before sintering it. Hydrothermal ageing treatment was applied to samples at 134°C for 5 h. STA analysis confirmed that the powder is binderfree. SEM and XRD analyses show homogeneous particle size and tetragonal as a major phase and monoclinic as a minor phase, respectively. BET method analysis shows a slight change in the pore size, pore volume and surface area of the powder samples, before and after heating at 400°C. Particle size distribution (SD) calculated from SEM images shows ∼ 40-50 nm particle size range of the powders. The results show that LTD was not observed in the powder after hydrothermal ageing treatment.

No abstract