TY  - JOUR
AU  - Akola, J.
AU  - Larrucea, J.
AU  - Jones, R. O.
TI  - Polymorphism in phase-change materials: melt-quenched and as-deposited amorphous structures in Ge_2 Sb_2 Te_5 from density functional calculations
JO  - Physical review / B
VL  - 83
IS  - 9
SN  - 1098-0121
CY  - College Park, Md.
PB  - APS
M1  - PreJuSER-14666
SP  - 094113
PY  - 2011
N1  - The calculations were performed on the Jugene (IBM Blue Gene/P) and Juropa (Intel Xeon 5570) computers in the FZ Julich with grants from the FZJ and the John von Neumann Institute for Computing (NIC). We thank A. Filipponi for calculating EXAFS from our partial PDF, S. Kohara, T. Matsunaga, and N. Yamada for discussions and support, and the Academy of Finland for funding.
AB  - The as-deposited (AD) amorphous structure of the prototype phase change material Ge2Sb2Te5 (GST-225) has been studied by density functional calculations for a 648-atom sample generated by computer-aided deposition at 300 K. The AD sample differs from a melt-quenched (MQ) sample in essential ways: (1) Ge atoms are predominantly tetrahedrally coordinated, and (2) homopolar and Ge-Sb bonds are more common and reduce the number of ABAB squares (A = Ge, Sb; B = Te), the characteristic building blocks of the material. The first observation resolves the contradiction between measured (EXAFS) and calculated Ge-Te bond lengths, and the latter explains the very different crystallization speeds. Sb and Te have higher chemical coordination than suggested by the "8-N rule" of covalent networks (N is the number of valence electrons). The EXAFS signal calculated for AD agrees much better with experiment than that calculated for MQ.
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000288211300003
DO  - DOI:10.1103/PhysRevB.83.094113
UR  - https://juser.fz-juelich.de/record/14666
ER  -