Structural and diffusion coefficient changes in amorphous Co-P Alloy

Journal of Materials Science and Engineering B 2 (8) (2012) 482-486

Structural and Diffusion Coefficient Changes in

Amorphous Co-P Alloy

Pham Huu Kien 1, Le Thi Huong Dung1

and Nguyen Van Dang2

1. Department of Physics, Thai Nguyen University of Education, Luong Ngoc Quyen street, Thai Nguyen Viet Nam

2. Department of Physics and Technology, College of Science, Thai Nguyen University, Thai Nguyen Vietnam

Received: June 18, 2012 / Accepted: August 10, 2012 / Published: August 25, 2012.

Abstract: Structural and diffusion coefficient changes in amorphous Co-P solids are studied using the statistic relaxation model

containing 105

atoms. The pair radial distribution functions of simulation model are agreement with experimental data. A large number

of simplexes have been found varying the relaxation degree and concentration of phosphorus. It found a significant number of bubbles,

they could break up and leads to diffusion. This simulation result reveals that the decrease in diffusion coefficient upon thermal

annealing and concentration of phosphorus observed experimentally for the most amorphous Co-P alloy is interpreted as a result of

reduced number of bubbles in system.

Key words: Statistic relaxation, amorphous alloys, tracer diffusion, simplex, bubbles.

1. Introduction

Amorphous alloy (AMA) Co-P is a material of much

technological relevance and has important implications

in material science and geophysics [1-9]. There are

many works studied the structural of AMA Co-P. For

example, J. F. Sadoc et al. shows that the first peak

position of the pair radial distribution functions (PRDF)

are at 2.55, 2.32 and 3.34 Å responding with Co-Co,

Co-P and P-P pairs, respectively. They showed that the

tetrahedral close packing model confirmed by the

Voronoi polyhedral study [4]. Y. Waseda reveals that

the atom distance and coordination number in

amorphous Co82P18 are equal to 2.57 Å, 10.0 and 2.30

Å, 8.0 responding with Co-Co, Co-P pairs, respectively.

He proposed a concentration dependent of the first

peak position in G(r) for binary alloy glasses with P

and B [5]. However, these works had not revealed the

structural dependent on relaxation degree and

concentration of metalloid.

Corresponding author: Pham Huu Kien, Doctor, research

fields: computational physics, simulation of amorphous

materials. E-mail: [email protected].

Furthermore, it is found that many specific

properties of diffusion in AMA Co-P compared to

crystal counterpart. Study in Refs. [6, 7] shows that the

tracer-diffusivity in well-relaxed specimen is much

slower than one in as-quenched sample. This relaxation

effect commonly is interpreted by the reduction of

quasi-vacancies in super-saturation until the relaxation

is over. In well-relaxed state, conversely, the tracer

atoms diffuse via collective movement of a group of

neighboring atoms. However, the experimental data in

Refs. [8, 9] is in contradiction to that the diffusion

mechanism just described predicted. Computer

simulation, on other hand reveals unstableness of

vacancies in amorphous matrix [10]. Previous study

shows that the atomic cage like bubble functions as

diffusion vehicle for AMA. The bubble represents a

spherical void with five or more atoms lied on its

surface [11]. However, the analysis of this study based

only on AMA Fe80B20.

Therefore, the present paper focus study the

structural and diffusion coefficient changes in AMA

Co-P upon metalloid concentration and relaxation

degree based on all types of simplexes and bubbles in