Berlin 2012 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

KR: Fachgruppe Kristallographie

KR 10: Crystallography in Nanoscience

KR 10.5: Talk

Thursday, March 29, 2012, 11:00–11:20, E 124

Crystal size and axial stress effects on the B4 to B1 phase transition pressure in AlN and ZnO nanocrystals investigated with second harmonic generation (SHG) — •Leonore Wiehl, Lkhamsuren Bayarjargal, and Björn Winkler — Institut für Geowissenschaften, Goethe-Universität, 60438 Frankfurt/Main, Germany

The transition pressure from the hexagonal (B4) to the cubic (B1) phase is shifted to higher pressures in nanocrystals when compared to bulk crystals for GaN, InN, CdSe or ZnO [1]. Only in AlN a shift to lower pressure was reported [2]. The influence of deviatoric stress was shown to reduce the transition pressure of bulk ZnO from 11 to 9.3 GPa [3]. Here, we present our results on nanocrystals of ZnO and AlN. Pressures up to 30 GPa were generated in diamond anvil cells (DACs), loaded with Ne gas for hydrostatic or KCl for non-hydrostatic conditions. The phase transition was detected by the vanishing of the second harmonic generation signal when going from the acentric (B4) to the centrosymmetric (B1) phase. Our results confirm the shift of transition pressures in nanocrystalline ZnO by 2-3 GPa to higher and in AlN by ∼10 GPa to lower pressures relative to the bulk crystals in accordance with the values reported [1,2] in the hydrostatic case. For the non-hydrostatic loadings transition pressures were reduced by 2-3 GPa. Financial support from the DFG (Ba 4020) is gratefully acknowledged.

[1] J. Z. Jiang et al., Europhys. Lett. 50 (2000) 48-53 [2] Z. Wang et al., J. Phys. Chem. B 108 (2004) 11506-11508 [3] L. Bayarjargal et al., Appl. Phys. Lett. 95 (2009) 061907(3p)