Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2011 Sep 28;135(12):124510. doi: 10.1063/1.3643327.
The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (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.
使用金刚石对顶砧中的高分辨率同步加速器 X 射线衍射，研究了晶态和非晶态 Ge(1)Sb(2)Te(4)（GST124）相变材料的相稳定性和相变的热力学性质随压力和温度的变化。发现立方相和六方相 GST124 相在压缩下的相变序列分别为：立方相→非晶相→正交相→体心立方相和六方相→正交相→体心立方相。六方相和体心立方相的熔化的克拉珀龙斜率分别为负和正，导致液相线存在压力依赖性最小值。综合来看，相平衡关系与该体系中存在多晶型性一致，沉积的非晶 GST 相是低熵低密度非晶相，而激光熔融淬火和高压非晶化的 GST 相是高熵高密度非晶相。这两种多晶型相之间的亚稳相界预计具有负的克拉珀龙斜率。
