Nanoglasses are solids consisting of nanometer-sized glassy regions connected by interfaces having a reduced density. We studied the structure of Sc(75)Fe(25) nanoglasses by electron microscopy, positron annihilation spectroscopy, and small-/wide-angle X-ray scattering. The positron annihilation spectroscopy measurements showed that the as-prepared nanoglasses consisted of 65 vol% glassy and 35 vol% interfacial regions. By applying temperature annealing to the nanoglasses and measuring in situ small-angle X-ray scattering, we observed that the width of the interfacial regions increased exponentially as a function of the annealing temperature. A quantitative fit to the small-angle X-ray scattering data using a Debye-Bueche random phase model gave a correlation length that is related to the sizes of the interfacial regions in the nanoglass. The correlation length was found to increase exponentially from 1.3 to 1.7 nm when the sample temperature was increased from 25 to 230 °C. Using simple approximations, we correlate this to an increase in the width of interfacial regions from 0.8 to 1.2 nm, while the volume fraction of interfacial regions increased from 31 to 44%. Using micro-compression measurements, we investigated the deformation behavior of ribbon glass and the corresponding nanoglass. While the nanoglass exhibited a remarkable plasticity even in the annealed state owing to the glass-glass interfaces, the corresponding ribbon glass was brittle. As this difference seems not limited to Sc(75)Fe(25) glasses, the reported result suggest that nanoglasses open the way to glasses with high ductility resulting from the nanometer sized microstructure.
Positron lifetime spectroscopy and cathodoluminescence were employed to study luminescence centers in
normalZnO
. The samples were high‐purity polycrystalline ceramics sintered at temperatures ranging from 800 to 1400°C for 2 to 40 h. Scanning electron microscopy shows that as annealing temperatures and/or times increase, the average grain size increases and can reach 30 μm for samples sintered at 1200°C. At the same time, the positron bulk lifetime approaches theoretically estimated single‐crystal values, while the integrated luminescence intensity increases significantly. A further increase of the sintering temperature beyond 1200°C results in a decrease in the luminescence intensity, in good agreement with the only weak luminescence observed in single‐crystalline material. The positron lifetime spectra clearly show the existence of one dominant vacancy‐type defect, most likely a complex involving
VnormalZn
, or the divacancy,
VnormalZnVO
, independent of sample thermal history. The concentration of this center steadily decreases with increasing sintering temperature. It is concluded that the yellow luminescence centers are related to charged zinc vacancies trapped in the grain boundary regions. We propose that the observed broadness of the spectra likely originates from the modification of the electronic configuration of the luminescence centers due to their complex environment. A direct connection between the positron and the luminescence results could not be established; instead, they appear to reflect two relatively independent aspects of the samples. It could be shown, however, that positron annihilation measurements can be used effectively to monitor the evolution of the microstructure of the samples, in good agreement with scanning electron micrographs.
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