Atomic scale characterization of SİAlON based materials through transmission electron microscopy (TEM) techniques

The goal of this thesis is to characterize the SiAlON based materials at atomic scale through a variety of transmission electron microscopy (TEM) techniques. For the first time in the literature, the results demonstrate that: (i) Yb and Ce atoms are preferentially incorporated into the ß-SiAlON crystal structure at the atom-specific interstitial lattice locations, yielding higher solubility for Yb than Ce; (ii) More expressly, Yb atoms take place in between two hexagonal rings, whereas Ce atoms mostly exist in the middle of hexagons; (iii) This observation is also confirmed in the Yb-Ce co-doped system; (iv) Ce atoms without any co-doped cation are present in the triangular-like host sites of ?-SiAlON unit-cell, accommodating much more atoms than interstitial hexagons in ß-SiAlON; (v) Yb and Ce atoms are periodically and differently arranged in the structure of intergranular films (IGFs) with only less than 1 nanometer thickness, explaining that they are in semi-crystalline nature, not completely amorphous;(vi) Yb and Ce atoms also constitute a clustered atomic transition-zone between the crystalline/amorphous interfaces, i.e., ?-ß SiAlONs/triple junctions; (vii) the Fe, Cr and Ti atoms enter in the ß-SiAlON crystal structure, leading a substitution mechanism in basic (Si,Al)(O,N)4 tetrahedrons, and (viii) the determination of highly luminescent character in Yb and Ce doped ß-SiAlON lattices strongly suggests the synthesis of ß-SiAlON:Yb+2 and ß:SiAlON:Ce+3 phosphors. Shortly, advanced TEM findings presented herein clearly show the visualization and identification of individual rare-earth and transition metal atoms in ?- and ß-SiAlON lattices, IGFs and interfaces. This capability offers new atomic-level engineering insights into how appropriate doping atoms and host SiAlON polymorphs should be chosen for tailoring of both next-generation SiAlON based structural and optical materials. It is also anticipated that the obtained results in this thesis will be applicable as guidelines for many kinds of rare-earth and transition metal atom doped materials using in different applications.