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Decagonal Phase (decagonal + phase)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Quasiperiodicity in decagonal phases forced by inclined net planes?

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2001
Walter Steurer
It is generally assumed that decagonal quasicrystals show periodically arranged atomic layers only on net planes perpendicular to the tenfold axis and quasiperiodically arranged ones parallel to it. However, there also do exist only slightly puckered atomic layers that are periodically arranged and inclined to the tenfold axis. They coincide with the net planes of the periodic average structures of the decagonal phase and are related to the strongest Bragg reflections. Since they link quasiperiodic and periodic directions, inclined net planes may play a crucial role for growth and stabilization of decagonal quasicrystals. In fact, it is shown how ideal quasiperiodic long-range order and inflation symmetry allow for the existence of inclined net planes with small corrugation and reinforce the relation with the periodic average structures. [source]

Structure solution of the basic decagonal Al,Co,Ni phase by the atomic surfaces modelling method

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2002
Antonio Cervellino
The atomic surfaces modelling technique has been used to solve the structure of the basic Ni-rich Al,Co,Ni decagonal phase. Formula Al70.6Co6.7Ni22.7, space group , five-dimensional unit-cell parameters: d1 = d4 = 4.752,(3),Å, d2 = d3 = 3.360,(2),Å, d5 = 8.1710,(2),Å; ,12 = ,34 = 69.295°, ,13 = ,24 = 45°, ,14 = 41.410°, ,23 = ,i5 = 90° (i = 1,4), V = 291.2,(7),Å5; Dx = 3.887,Mg,m,3. Refinement based on |F|; 2767 unique reflections (|F| > 0), 749 parameters, R = 0.17, wR = 0.06. Describing the structure of quasicrystals embedded in n -dimensional superspace in principle takes advantage of n -dimensional periodicity to select the minimal set of degrees of freedom for the structure. The method of modelling of the atomic surfaces yielded the first fully detailed structure solution of this phase. Comparison with numerous former, less accurate models confirms several features already derived, but adds a new essential insight of the structure and its complexity. The atoms fill the space forming recurrent structure motifs, which we will (generically) refer to as clusters. However, no unique cluster exists, although differences are small. Each cluster shows a high degree of structural disorder. This gives rise to a large configurational entropy, as much as expected in a phase which is stable at high temperature. On the other side, the cluster spatial arrangement is perfectly quasiperiodic. These considerations, corroborated by analysis of the structural relationship with neighbouring periodic phases, strongly suggest the existence of a non-local, long-range interaction term in the total energy which may be essential to the stability. [source]

A symmetrical indexing scheme for decagonal quasicrystals analogous to Miller,Bravais indexing of hexagonal crystals

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2007
S. Ranganathan
The problems of redundancy and superfluous indices in indexing the planes and axes in a decagonal quasicrystal are considered, using a scheme of five coplanar vectors in the quasiperiodic plane and one perpendicular vector. Of all the indexing schemes in use, this scheme offers the maximum advantage. An analogy is drawn to the hexagonal system using Miller,Bravais indices. Based on this, a symmetry-based indexing system for decagonal phases is devised that follows a simplified approximate zone law analogous to the exact zone law for the hexagonal case. The indices based on this scheme will be designated as `Frank indices'. High-symmetry electron diffraction zone-axis patterns as well as powder X-ray diffraction patterns are indexed using Frank indices and compared with those of other indexing schemes. [source]