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Ni-substitution induced inversion in ZnFe_2O_4 seen by positron annihilation

机译：正电子an没观察到Ni取代引起ZnFe_2O_4的反转

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摘要

We report in this work about the inversion of the spinel structure of ZnFe_2O_4 induced by the substitution of Zn~(2+) by Ni~(2+) ions. Positron lifetimes were measured in Zn_(1-x)Ni_xFe_2O_4 with different concentrations (x) of Ni~(2+) ions and a drastic change across x = 0.4 - 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni~(2+) is smaller in size than Zn~(2+), defects due to non-stoichiometry are less in ZnFe_2O_4 than in ZnFe_2O_4. The increase in positron lifetime implies the trapping of positrons being shifted from A-to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.
机译：我们在这项工作中报告了由Zn〜（2+）被Ni〜（2+）离子取代引起的ZnFe_2O_4的尖晶石结构反转。在具有不同浓度（x）的Ni〜（2+）离子的Zn_（1-x）Ni_xFe_2O_4中测量正电子寿命，并且观察到x = 0.4-0.6的急剧变化，这归因于这种转变。掺杂时阳离子位置的互换使得其中一小部分未被占用，这些空位充当了正电子俘获中心。由于Ni〜（2+）的尺寸小于Zn〜（2+），因此非化学计量引起的缺陷在ZnFe_2O_4中比在ZnFe_2O_4中少。正电子寿命的增加意味着正电子的俘获从A位转移到B位，并且表明从反尖晶石构型转变为正常的尖晶石构型。巧合多普勒展宽的测量结果支持了这些发现。

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