Köck Eva-Maria, Kogler Michaela, Götsch Thomas, Schlicker Lukas, Bekheet Maged F, Doran Andrew, Gurlo Aleksander, Klötzer Bernhard, Petermüller Benedikt, Schildhammer Daniel, Yigit Nevzat, Penner Simon
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria.
Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften- und technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany.
Dalton Trans. 2017 Apr 5;46(14):4554-4570. doi: 10.1039/c6dt04847a.
The surface chemical properties of undoped tetragonal ZrO and the gas-phase dependence of the tetragonal-to-monoclinic transformation are studied using a tetragonal ZrO polymorph synthesized via a sol-gel method from an alkoxide precursor. The obtained phase-pure tetragonal ZrO is defective and strongly hydroxylated with pronounced Lewis acidic and Brønsted basic surface sites. Combined in situ FT-infrared and electrochemical impedance measurements reveal effective blocking of coordinatively unsaturated sites by both CO and CO, as well as low conductivity. The transformation into monoclinic ZrO is suppressed up to temperatures of ∼723 K independent of the gas phase composition, in contrast to at higher temperatures. In inert atmospheres, the persisting structural defectivity leads to a high stability of tetragonal ZrO, even after a heating-cooling cycle up to 1273 K. Treatments in CO and H increase the amount of monoclinic ZrO upon cooling (>85 wt%) and the associated formation of either Zr-surface-(oxy-)carbide or dissolved hydrogen. The transformation is strongly affected by the sintering/pressing history of the sample, due to significant agglomeration of small crystals on the surface of sintered pellets. Two factors dominate the properties of tetragonal ZrO: defect chemistry and hydroxylation degree. In particular, moist conditions promote the phase transformation, although at significantly higher temperatures as previously reported for doped tetragonal ZrO.
使用通过溶胶 - 凝胶法由醇盐前驱体制备的四方ZrO多晶型物，研究了未掺杂四方ZrO的表面化学性质以及四方相向单斜相转变的气相依赖性。所获得的纯相四方ZrO存在缺陷且强烈羟基化，具有明显的路易斯酸性和布朗斯特碱性表面位点。原位傅里叶变换红外光谱和电化学阻抗联合测量表明，CO和CO对配位不饱和位点均有有效阻断作用，且电导率较低。与较高温度下的情况相反，在高达约723 K的温度下，四方ZrO向单斜ZrO的转变受到抑制，与气相组成无关。在惰性气氛中，即使经过高达1273 K的加热 - 冷却循环，持续存在的结构缺陷导致四方ZrO具有高稳定性。在CO和H中处理后，冷却时单斜ZrO的量增加（>85 wt%），并伴随形成Zr表面（氧）碳化物或溶解氢。由于烧结球粒表面小晶体的大量团聚，转变受到样品烧结/压制历史的强烈影响。两个因素主导四方ZrO的性质：缺陷化学和羟基化程度。特别是，潮湿条件促进了相变，尽管温度比先前报道的掺杂四方ZrO要高得多。
