Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials

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Kalkan B. , Sen S., Clark S. M.

JOURNAL OF CHEMICAL PHYSICS, cilt.135, 2011 (SCI İndekslerine Giren Dergi) identifier identifier identifier

  • Cilt numarası: 135 Konu: 12
  • Basım Tarihi: 2011
  • Doi Numarası: 10.1063/1.3643327


The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge1Sb2Te4 (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic -> amorphous -> orthorhombic -> bcc and hexagonal -> orthorhombic -> bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. (C) 2011 American Institute of Physics. [doi:10.1063/1.3643327]