A vacuum environment is usually preferred for reducing the dwell time and sintering temperature for doped zirconia ceramics. However, for the present work with 10 mol.% CaO-doped ZrO₂ (10CaSZ) ceramics, both hot-pressing and vacuum sintering techniques yielded ceramics with open pores (ρ ∼ 93%) and significant amounts of the deleterious monoclinic phase ($>$50%). This is in stark contrast with the conventionally sintered highly dense (>99%) 10CaSZ ceramics, where only tetragonal and cubic phases were noted. Probing via electron paramagnetic resonance (EPR) depicted the trapping of oxygen vacancies by vacancies generated in vacuum at high temperature. A possible change in the local coordination (of ions) and the subsequent chemical environment was confirmed by the observed asymmetric signal shape and broader linewidth of the EPR signals. Potential loss of oxygen and deviation from stoichiometry (for dopant) was confirmed via EPR analysis along with the support of energy dispersive spectra analysis. Despite no noticeable shift in the XRD pattern for Ca²⁺ depletion, the observed compositional gradient differences in the calcium elemental mapping suggested dopant segregation at the grain boundaries. The conclusions from the present work point toward specificity of a given materials system for its beneficial densification under hot pressing or vacuum sintering.

中文翻译：

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10 mol.% CaO 掺杂氧化锆陶瓷热压和真空烧结过程中问题的探讨

通常优选真空环境来减少掺杂氧化锆陶瓷的停留时间和烧结温度。然而，对于目前使用 10 mol.% CaO 掺杂 ZrO ₂ (10CaSZ) 陶瓷的研究，热压和真空烧结技术都产生了具有开孔 ( ρ ∼ 93%) 和大量有害单斜晶相的陶瓷 ($>$50%）。这与传统烧结的高致密 (>99%) 10CaSZ 陶瓷形成鲜明对比，后者仅观察到四方相和立方相。通过电子顺磁共振（EPR）探测描述了高温真空中产生的空位对氧空位的捕获。通过观察到的 EPR 信号的不对称信号形状和更宽的线宽，证实了（离子）局部配位和随后的化学环境可能发生的变化。通过 EPR 分析以及能量色散谱分析的支持，确认了氧的潜在损失和化学计量的偏差（对于掺杂剂）。尽管Ca ²⁺耗尽的XRD 图案没有明显变化，但在钙元素映射中观察到的成分梯度差异表明掺杂剂在晶界处偏析。目前工作的结论表明给定材料系统在热压或真空烧结下有利于致密化的特殊性。