Influence of high pressure on the polytype structure of nanocrystalline GaN

Roman Pielaszek 3,4Stanisław Gierlotka 4Ewa Grzanka 3,4Svitlana Stelmakh 4Bogdan F. Palosz 4

1. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland
2. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
3. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland
4. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland


High-pressure in-situ diffraction studies of nanocrystalline (20 nm in
diameter) pure-hexagonal GaN were performed up to 20 GPa in Diamond
Anvil Cell (DAC, station F3 at Hasylab, Hamburg). It was found that
high-pressure treatment leads to transitions in polytype structure of
nanocrystalline GaN.
A simple model of introduction of stacking faults by random shifts of
(0001) planes was used for simulation of strain-induced disordering
process in nanocrystals.
Polytype structures resulting from simulation of disordering process
were applied to create atomic models of GaN crystallites (up to 16 nm
in diameter). Powder diffraction patterns were calculated for those
crystallites using Debye formula in its literal form.
A good agreement between diffraction patterns simulated by introducing
0.8-1.2 Shifts Per Layer (SPL) and those experimentally measured under
pressures of 14-20 GPa has been obtained.
The model proposed might explain why disordering arises in small
grains under high pressure.
Hypothetical high-pressure behavior of 2H, 3C, 4H, 6H and 8H polytypes
is also discussed.
This work was supported by the State Committee for Scientific
Research, Grants No. 7/T08A/036/18 and 7/T08A/030/19.


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Presentation: poster at High Pressure School 2001 (4th), by Roman Pielaszek
See On-line Journal of High Pressure School 2001 (4th)

Submitted: 2003-02-16 17:33
Revised:   2009-06-08 12:55