Formation process of periodic non-conservative antiphase boundary structure in L-Pd5Ce

1990 ◽  
Vol 48 (4) ◽  
pp. 162-163
Author(s):  
Masaru Itakura ◽  
Noriyuki Kuwano ◽  
Kensuke Oki
Keyword(s):  
Formation Process ◽  
Domain Size ◽  
Antiphase Boundary ◽  
Boundary Structure ◽  
Temperature Phase ◽  
Arc Melting ◽  
Iced Water ◽  
Antiphase Domains ◽  
Low Temperature Phase ◽  
Degree Of Order

The low temperature phase of Pd5Ce (L-Pd5Ce) has a one-dimensional long period superstructure (1D-LPS) derived from Ll2. The periodic antiphase boundaries (APBs) are parallel to (110) planes and have a shift vector of 1/2[110]. Hereafter, the indices are referred to the basic lattices of Ll2 As insertion of the APB causes a change in composition, such an APB is called “non-conservative”. Then, a domain size M depends upon the Ce concentration in the alloy. It was found that M increases also with temperature. The temperature dependency of M is attributed to a change of the degree of order within the antiphase domains. In this work, morphology of the non-conservative APBs is observed to clarify the formation process of the 1D-LPS.The alloy of Pd-16.7 at%Ce was prepared by arc melting in argon atmosphere. Disc specimens made from the alloy ingot were first held at 985 K for 260 ks and quenched in iced water to obtain the state of M=∞ or Ll2, followed by annealing for various lengths of time. The annealing temperature was 873 K where the equilibrium value for M is about 3 in unit of (110) lattice spacing of Ll2. Observation was carried out using microscopes JEM-2000FX, JEM-4000EX (HVEM Lab., Kyushu Univ.) and JEM-2000EX (Dept. of Mater. Sci. Tech., Kyushu Univ.).

Molecular dynamics simulation of the phase transition in adamantane

1988 ◽  
Vol 66 (4) ◽  
pp. 1018-1025 ◽  
Author(s):  
A. S. Trew ◽  
G. S. Pawley
Keyword(s):  
Orientational Order ◽  
Significant Degree ◽  
Phase Changes ◽  
Dynamics Simulation ◽  
Local Order ◽  
Temperature Phase ◽  
Orientational Distribution ◽  
Molecule Model ◽  
Low Temperature Phase ◽  
Degree Of Order

Phase changes in adamantane have been studied by MD simulation on the DAP computers, using a zero-pressure technique to simulate clusters of 128 and 256 molecules where each member interacts with all others via the rigid molecule model and the 6-exp atom–atom potential. The form of the potential has been modified to permit the use of the 16 hydrogen sites only, giving a 65% saving in the calculation times. This model is shown to give lattice dynamics of adamantane closely similar to results with potentials which are generally accepted.Using this potential the system equilibrates into the correct low temperature phase [Formula: see text] and on heating, a transition is observed at 210 ± 10 K to an Fm3m phase where the molecules lie preferentially in the Td orientations, as expected. Further heating beyond 240 ± 15 K removes all apparent orientational order, though the underlying lattice is still fcc. On recooling the cluster from 300 to 100 K the orientational distribution function developed a significant degree of order as determined through the calculation of a correlation function designed to show any local order. This order is consistent with the lowest phase structure, but would in itself be insufficient to suggest a particular crystal structure.

Morphology of Bi2O3 Nanowires and Nanoflowers in the Synthesis of MnBi Alloys

2018 ◽  
Vol 283 ◽  
pp. 124-131
Author(s):  
Thanida Charoensuk ◽  
Chitnarong Sirisathitkul ◽  
Upsorn Boonyang ◽  
Pongsakorn Jantaratana
Keyword(s):  
Energy Dispersive Spectrometry ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Melting Points ◽  
Subsequent Formation ◽  
X Ray ◽  
Arc Melting ◽  
Potential Applications ◽  
Low Temperature Phase ◽  
Hard Magnetic Properties

High temperature phase (HTP) MnBi alloys were formed using the arc-melting method. The drastic difference in the melting points of Mn and Bi resulted in non-homogeneity. The MnBi, Mn, Bi and O were detected by energy dispersive spectrometry (EDS). The field emission scanning electron microscope (FESEM) revealed the morphology of each phase. The rod-like and flower-like nanostructures were consistent with Bi2O3 as indicated by EDS and X-ray diffactometry. The HTP MnBi was transformed to the low temperature phase (LTP) following the annealing process. The remaining Bi and Mn are susceptible to oxidation leading to the subsequent formation of Bi2O3 as well as MnO. Whereas LTP MnBi alloys are useful for their hard magnetic properties, Bi2O3 nanowire is receiving attention for potential applications in optoelectronic devices.

TEM investigation of the low temperature phase of HfV2

1995 ◽  
Vol 53 ◽  
pp. 252-253
Author(s):  
F. Chu ◽  
T. E. Mitchell
Keyword(s):  
Low Temperature ◽  
Lattice Parameter ◽  
Laves Phase ◽  
Temperature Phase ◽  
Arc Melting ◽  
Cold Stage ◽  
Phase Intermetallic ◽  
Preliminary Study ◽  
Diffraction Patterns ◽  
Low Temperature Phase

C15 Laves phase intermetallic compounds are potential high temperature structural materials, of which C15 HfV2 is particularly attractive. At room temperatures (RT), the C15 Laves phase has a fcc-based structure with a lattice parameter a=7.4 Å, as shown in Fig. 1. Sensitive specific heat measurements indicate that HfV2 undergoes a structural transformation at 115 K, as shown in Fig. 2. The crystal structure of the low temperature (LT) phase of HfV2 is not unambiguously known, although some studies have been done. A HfV2 alloy was made by arc-melting. The alloy was homogenized at 1200°C for 120h. In a preliminary study we have concentrated on selected area diffraction patterns (SADs) along different zone axes of C15 structure at 83 K, using a Philips CM 30 microscope with a liquid nitrogen cold stage.A <100>C15 SAD at RT is shown in Fig. 3 (a). At 83 K, SADs along some <100>C15 show (100), (200), and (300) superlattice spots, as shown in Fig 3 (b), while SADs along other <100>C15 indicate (110) and (200) superlattice spots, as shown in Fig. 3 (c).

scholarly journals Cu-Au Alloys Using Monte Carlo Simulations and the BFS Method for Alloys

1995 ◽  
Vol 408 ◽  
Author(s):  
Guillermo Bozzolo ◽  
Brian Good ◽  
John Ferrante
Keyword(s):  
Monte Carlo ◽  
Low Temperature ◽  
Antiphase Boundary ◽  
Temperature Phase ◽  
Ordered Structures ◽  
Smith Method ◽  
Properties Of Materials ◽  
Materials Used ◽  
Semi Empirical ◽  
Low Temperature Phase

AbstractSemi empirical methods have shown considerable promise in aiding in the calculation of many properties of materials [1,2]. Materials used in engineering applications have defects that occur for various reasons including processing [3]. In this work we present the first application of the BFS (Bozzolo, Ferrante and Smith) method for alloys [1] to describe some aspects of microstructure due to processing for the Cu-Au system (Cu-Au, CuAu3 , and Cu3Au). We use finite temperature Monte Carlo calculations, in order to show the influence of ’heat treatment‘ in the low-temperature phase of the alloy. Although relatively simple, it has enough features that could be used as a first test of the reliability of the technique. The main questions to be answered in this work relate to the existence of low temperature ordered structures for specific concentrations, for example, the ability to distinguish between rather similar phases for equiatomic alloys (CuAu I and CuAu II, the latter characterized by an antiphase boundary separating two identical phases).

On the sequence of three related phases of [Ni(H2O)2(15-crown-5)](HSO4)2 in the temperature range 110–295 K

2010 ◽  
Vol 66 (4) ◽  
pp. 430-440 ◽  
Author(s):  
Maxime A. Siegler ◽  
Eli Stavitski
Keyword(s):  
Structural Changes ◽  
Crystal Packing ◽  
Solid Phase ◽  
Significant Loss ◽  
Phase Iii ◽  
Temperature Phase ◽  
Phase Sequence ◽  
Analogous Compound ◽  
Low Temperature Phase ◽  
Degree Of Order

Attempts to prepare the compound [Ni(H2O)2(15-crown-5)](X)2 were eventually successful with X = NO_3^- provided that a synthetic route aimed at restricting water was followed. Application of this method was extended to make the analogous compound with X = HSO_4^-, for which three symmetry-related phases were isolated between 295 and 110 K: a room-temperature phase with Z′ = ½ [phase (I)], an intermediate-temperature phase with Z′ = 1 [phase (II)] and a low-temperature phase with Z′ = 2 [phase (III)]. The phases are related by two reversible solid–solid phase transitions, and both transitions take place without a significant loss of crystallinity. In the phase sequence (I) ↔ (II) ↔ (III) (Z′: ½ ↔ 1 ↔ 2), the crystal packing remains remarkably similar but the degree of order in the crystal changes significantly; the structure is very disordered at room and intermediate temperatures but is ordered at 110 K. The compound [Ni(H2O)2(15-crown-5)](HSO4)2 has a complicated hydrogen-bonding network, which contains O—H...O bonds between the counterions. Structural changes are largest along some face-diagonal directions in the sequence (I) ↔ (II) ↔ (III).

Determination of the lattice translation across {110} APBs in GaAs

1988 ◽  
Vol 46 ◽  
pp. 600-601
Author(s):  
D.R. Rasmussen ◽  
N.-H. Cho ◽  
C.B. Carter
Keyword(s):  
Grain Boundaries ◽  
Lower Energy ◽  
Antiphase Boundary ◽  
The Other ◽  
Boundary Structure ◽  
Interface Plane ◽  
Inversion Symmetry ◽  
High Angle ◽  
Equilibrium Distance

Domains in GaAs can exist which are related to one another by the inversion symmetry, i.e., the sites of gallium and arsenic in one domain are interchanged in the other domain. The boundary between these two different domains is known as an antiphase boundary [1], In the terminology used to describe grain boundaries, the grains on either side of this boundary can be regarded as being Σ=1-related. For the {110} interface plane, in particular, there are equal numbers of GaGa and As-As anti-site bonds across the interface. The equilibrium distance between two atoms of the same kind crossing the boundary is expected to be different from the length of normal GaAs bonds in the bulk. Therefore, the relative position of each grain on either side of an APB may be translated such that the boundary can have a lower energy situation. This translation does not affect the perfect Σ=1 coincidence site relationship. Such a lattice translation is expected for all high-angle grain boundaries as a way of relaxation of the boundary structure.

Sign in / Sign up

Export Citation Format

Share Document