Abstract
Herein we demonstrate the specifics of using the positron annihilation lifetime spectroscopy (PALS) method for the study of free volume changes in functional ceramic materials. Choosing technological modification of nanostructured MgAl2O4 spinel as an example, we show that for ceramics with well-developed porosity positron annihilation is revealed through two channels: positron trapping channel and ortho-positronium decay. Positron trapping in free-volume defects is described by the second component of spectra and ortho-positronium decay process by single or multiple components, depending on how well porosity is developed and on the experimental configuration. When using proposed positron annihilation lifetime spectroscopy approaches, three components are the most suitable fit in the case of MgAl2O4 ceramics. In the analysis of the second component, it is shown that technological modification (increasing sintering temperature) leads to volume shrinking and decreases the number of defect-related voids. This process is also accompanied by the decrease of the size of nanopores (described by the third component), while the overall number of nanopores is not affected. The approach to the analysis of positron annihilation lifetime spectra presented here can be applied to a wide range of functional nanomaterials with pronounced porosity.
Highlights
IntroductionPositron annihilation lifetime spectroscopy (PALS) technique is considered as one of the promising alternative methods to analyze free volume and defects in functional and other materials [1,2,3,4,5], including ceramics [6,7,8], glasses [9,10,11], polymers [12,13,14], nanocomposites [15,16,17], etc
During 2 h exhibits reflexes of three phases: along with the principal MgAl2 O4 spinel phase, there are MgO (11.25% for the ceramics sintered at 1100 ◦ C and 5.82% for the ceramics sintered at 1200 ◦ C) and Al2 O3
MgAl2 O4 ceramics can be achieved with the three-component fitting procedure
Summary
Positron annihilation lifetime spectroscopy (PALS) technique is considered as one of the promising alternative methods to analyze free volume and defects in functional and other materials [1,2,3,4,5], including ceramics [6,7,8], glasses [9,10,11], polymers [12,13,14], nanocomposites [15,16,17], etc. In the frame of this model, the second component describes capturing of positrons by free volume defects such as vacancy clusters, neutral surfaces of powder particles, or vacancies with a negative charge, those that are close to grain boundaries. The shortest component is related to the annihilation of the defect-free mass
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
