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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Transformation of tetragonal zirconia phase to monoclinic phase in the presence of Fe~(3+) ions as probes: an EPR study
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Transformation of tetragonal zirconia phase to monoclinic phase in the presence of Fe~(3+) ions as probes: an EPR study

机译：Fe〜（3+）离子存在下四方氧化锆相向单斜晶相的转变：EPR研究

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摘要

EPR was mainly used to study the morphological, textural and structural behavior of zirconium hydroxide [ZrO(OH)_2] with respect to calcination under air at different temperatures. For calcination temperatures less than 700 deg C, the tetragonal and monoclinic phases of the solid were present. In this range of temperatures an EPR signal with g_(xx) = 1.9755, g_(yy) = 1.9720 and g_(zz) = 1.9562 was observed and attributed to Zr~(3+) ions located in octahedral sites with strong tetragonal distortion. The dehydration of OH~- groups from solids could be responsible for the Zr~(4+) reduction into Zr~(3+) ions. A second signal, centered at g = 2.0018, was also observed and assigned to trapped single electrons located in oxygen vacancies of ZrO_2. A third signal with g_(xx) = 2.0040, g_(yy) = 2.0082 and g_(zz) = 2.0334 was attributed to adsorbed O_2~- species. Finally, a fourth signal obtained at low magnetic field with different g values was attributed to Fe~(3+) ions located in sites with a purely rhombic field. For high calcination temperatures (> 700deg C), the tetragonal phase was completely transformed into monoclinic phase. In this phase, the trapped single electrons and the adsorbed O_2~- species disappeared whereas the number of Zr~(3+) ions increases when compared to that obtained at lower calcination temperatures. This increase could be related to the reduction of Zr~(4+) by the trapped single electrons and the formation of the monoclinic phase which stabilizes the Zr~(3+) ions. In this latter phase, the Fe~(3+) ions are located in sites which have the same environmental symmetry than in tetragonal phase but with specific EPR parameter values.
机译：EPR主要用于研究氢氧化锆[ZrO（OH）_2]在空气中在不同温度下煅烧的形态，结构和结构行为。对于低于700℃的煅烧温度，存在固体的四方相和单斜相。在此温度范围内，观察到EPR信号g_（xx）= 1.9755，g_（yy）= 1.9720和g_（zz）= 1.9562，并且归因于Zr〜（3+）离子位于八面体位置，具有强烈的四方畸变。 OH〜-从固体中的脱水可能是Zr〜（4+）还原成Zr〜（3+）离子的原因。还观察到以g = 2.0018为中心的第二个信号，并将其分配给位于ZrO_2的氧空位中的捕获单电子。 g_（xx）= 2.0040，g_（yy）= 2.0082和g_（zz）= 2.0334的第三信号归因于吸附的O_2〜-物种。最后，在低磁场下获得的具有不同g值的第四信号归因于位于纯菱形场中的Fe〜（3+）离子。对于高煅烧温度（> 700℃），四方相完全转变为单斜晶相。与在较低的煅烧温度下获得的Zr〜（3+）离子相比，在此阶段中被捕获的单电子和被吸附的O_2〜-种类消失了，而Zr〜（3+）离子的数量却增加了。这种增加可能与被捕获的单电子还原Zr〜（4+）和形成稳定Zr〜（3+）离子的单斜晶相有关。在后一相中，Fe〜（3+）离子位于与四方相具有相同环境对称性但具有特定EPR参数值的位置。

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