A TEM study on ZrO₂-rich phases in the quasibinary system ZrO₂-Zr₃N₄: Comparison between fast and slowly cooled samples

Abstract

A thorough comparison between the slowly and fast cooled ß"-type oxynitrides of zirconium has been carried out by means of transmission electron microscopy. This work aims at detecting and analyzing the so-called "modulated" β'' phase, which has been involved in the introduction of ordered anion vacancies through nitridation of zirconia. The gained information from the occurrence of such a modulated phase and the manner, in what it appears, do support the suggested structure model, which had been developed in early works in order to get a better understanding of the typical phase transitions in zirconium oxynitrides.*

Nitrogen-doped zirconia: A comparison with cation stabilized zirconia

“…The b-type phases ðb; b 0 ; b 00 , etc.) in nitrogen-doped zirconia can be described as arrangements of Bevan clusters containing [1 1 1] vacancy pair and perfect fluorite unit [7,9,13,[38][39][40]]. An indication of N/O ordering was also found in the b 0 -phase in the Mg-Zr-O-N system [41].…”

“…Vacancy ordered structures consisting of so-called Bevan clusters or [1 1 1] vacancy pairs, as observed in Y-or Scdoped zirconia, are the pronounced feature in nitrogencontaining zirconia [3,7,13,38]. The b-type phases ðb; b 0 ; b 00 , etc.)…”

“…Within the last decade N-containing zirconia has been drawing renewed attention [1][2][3][4][5] while prior studies date back to the sixties [6][7][8][9]. Most notable in recent studies was the finding that in the presence of a small amount of Y (2 or 3 mol% Y 2 O 3 Þ N successfully stabilizes zirconia in tetragonal and cubic phases even at low temperatures [1,2,4,5,10,11], while Ndoping alone results in the formation of ordered-vacancy phases in rhombohedral or primitive trigonal structures below 1000 C [12,13].…”

The impact of nitrogen mobility on the activity of zirconium oxynitride catalysts for ammonia decomposition

“…Whereas the β phase is strongly disordered, the β phase exhibits ordered anion vacancies [6,7]. Moreover, the β ZrON phase contains a larger amount of nitrogen ions in the lattice than the β phase, accompanied by an increased number of vacancies in the oxygen sublattice [7,8]. Apparently, phase demixing requires mobility of nitrogen ions in the ZrON structure to enable migration of nitrogen ions and the formation of β ZrON and ZrO 2 .…”

“…The β and β phases can be described as anion-deficient fluorite structures. Whereas the β phase is strongly disordered, the β phase exhibits ordered anion vacancies [6,7]. Moreover, the β ZrON phase contains a larger amount of nitrogen ions in the lattice than the β phase, accompanied by an increased number of vacancies in the oxygen sublattice [7,8].…”