Abstract:The (GeTe)1−γ–(Sb2Te3)γ pseudobinary system has, over almost its entire composition range, two kinds of crystalline phase: one is a metastable phase with a NaCl-type structure and the other is a spectrum of stable phases with homologous structures. In the metastable phase, Ge/Sb atoms and intrinsic vacancies occupy the Na sites; on the other hand, Te atoms are located at the Cl sites. These vacancies are produced by following γ/1+2γ to ensure the stoichiometry of the metastable pseudobinary compound. This meta… Show more
“…These measurements do not distinguish between Ge-Te and Sb-Te bonds and give 2.88 and 3.10 Å for the shorter and longer bonds, most of which are Ge-Te. 4 These values are 1%-2% shorter than the PBE results for GST-225. The calculated cohesive energy of crystalline GST-8,2,11 is 3.02 eV, and the melt-quenched amorphous sample is 0.084 eV/atom higher in energy.…”
Section: Methods Of Calculationmentioning
confidence: 77%
“…It is astonishing that almost nothing is known about the amorphous structure of GST-8,2,11, a material now used for the third generation optical storage, BD. 4 Until very recently, this observation applied to the amorphous phases of almost all PCMs.…”
Section: Introductionmentioning
confidence: 99%
“…GeTe-rich alloys with small values of x are better and it has been found that the optical contrast between the two phases increases monotonically as x → 0. 4 On the other hand, it has been known for many years that the most rapid crystallization occurs for larger values of x, as in GeSb 4 Te 7 ͑x = 2 3 ͒. Compromises are necessary, and Ge 8 Sb 2 Te 11 ͑GST-8,2,11, x = 1 9 ͒ is a material of choice for BD.…”
Section: Introductionmentioning
confidence: 99%
“…Compromises are necessary, and Ge 8 Sb 2 Te 11 ͑GST-8,2,11, x = 1 9 ͒ is a material of choice for BD. 4 The amorphous-crystalline phase change cannot be understood without knowing the structures involved. The crystalline phases of GeTe-rich alloys in the family ͓͑GeTe͒ 1−x ͑Sb 2 Te 3 ͒ x , x Յ 1 3 ͔ have been studied for many years.…”
Section: Introductionmentioning
confidence: 99%
“…In most cases there is a metastable phase with a distorted NaCl structure and a higher temperature phase with homologous structures. 4 Vacancies play an essential role in stabilizing the NaCl structure over a wide range of x. 5 Density-functional calculations have been performed for crystalline structures with compositions ͑GeTe͒ 1−x ͑Sb 2 Te 3 ͒ x and nearby stoichiometries.…”
“…These measurements do not distinguish between Ge-Te and Sb-Te bonds and give 2.88 and 3.10 Å for the shorter and longer bonds, most of which are Ge-Te. 4 These values are 1%-2% shorter than the PBE results for GST-225. The calculated cohesive energy of crystalline GST-8,2,11 is 3.02 eV, and the melt-quenched amorphous sample is 0.084 eV/atom higher in energy.…”
Section: Methods Of Calculationmentioning
confidence: 77%
“…It is astonishing that almost nothing is known about the amorphous structure of GST-8,2,11, a material now used for the third generation optical storage, BD. 4 Until very recently, this observation applied to the amorphous phases of almost all PCMs.…”
Section: Introductionmentioning
confidence: 99%
“…GeTe-rich alloys with small values of x are better and it has been found that the optical contrast between the two phases increases monotonically as x → 0. 4 On the other hand, it has been known for many years that the most rapid crystallization occurs for larger values of x, as in GeSb 4 Te 7 ͑x = 2 3 ͒. Compromises are necessary, and Ge 8 Sb 2 Te 11 ͑GST-8,2,11, x = 1 9 ͒ is a material of choice for BD.…”
Section: Introductionmentioning
confidence: 99%
“…Compromises are necessary, and Ge 8 Sb 2 Te 11 ͑GST-8,2,11, x = 1 9 ͒ is a material of choice for BD. 4 The amorphous-crystalline phase change cannot be understood without knowing the structures involved. The crystalline phases of GeTe-rich alloys in the family ͓͑GeTe͒ 1−x ͑Sb 2 Te 3 ͒ x , x Յ 1 3 ͔ have been studied for many years.…”
Section: Introductionmentioning
confidence: 99%
“…In most cases there is a metastable phase with a distorted NaCl structure and a higher temperature phase with homologous structures. 4 Vacancies play an essential role in stabilizing the NaCl structure over a wide range of x. 5 Density-functional calculations have been performed for crystalline structures with compositions ͑GeTe͒ 1−x ͑Sb 2 Te 3 ͒ x and nearby stoichiometries.…”
Phase‐change materials (PCMs) are chemical ingredients for diverse data storage and data processing applications. They can be rapidly and reversibly switched between crystalline and amorphous phases, and a pronounced contrast in physical properties between both phases is used to encode digital “ones” and “zeroes.” In this chapter, we review the solid‐state chemistry (and physics) of Ge–Sb–Te alloys that are among the most promising PCMs and are widely used from rewriteable Blu‐ray disks to prototypes for future memory technologies. The atomic structures of crystalline and amorphous Ge–Sb–Te alloys are reviewed in sequence, and it is shown how the fundamental microscopic nature of these materials can be directly linked to unconventional and technologically valuable properties. An outlook onto emerging applications of Ge–Sb–Te PCMs is finally given, exemplifying the diversity and usefulness of this class of solid‐state materials.
Phase‐change materials (PCMs) are widely used for data storage and in other functional devices. Despite their seemingly simple compositions, these materials exhibit intriguing microscopic complexity and a portfolio of interesting properties. In this Feature Article, it is shown that structural and electronic peculiarities on the atomic scale are key determinants for the technological success of PCMs. Particular emphasis is put on the interplay of different experimental and theoretical methods, on the bonding nature of crystalline and amorphous PCMs, and on the role of surfaces and nanostructures. Then, unconventional transport properties of the crystalline phases are highlighted, both with regard to electrical and heat conduction. Finally, perspectives and future directions are drawn: for finding new PCMs based on microscopic understanding, and also for new applications of these materials in emerging fields.
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