Question

The memory metal, nitinol, is an alloy of nickel and titanium. It is called a memory metal because after being deformed, a piece of nitinol wire will return to its original shape. (See Chemmatters, October 1993, pp. 4–7.) The structure of nitinol consists of a simple cubic arrayof Ni atoms and an inner penetrating simple cubic array of Ti atoms. In the extended lattice, a Ti atom is foundat the center of a cube of Ni atoms; the reverse is also true.

a. Describe the unit cell for nitinol.

b. What is the empirical formula of nitinol?

c. What are the coordination numbers (number of nearest neighbors) of Ni and Ti in nitinol?

Short answer

a) The unit cell consists of Ni at the cube corners and Ti at the body center or Ti at the cube corners and Ni at the body center.

b) 8 ×1 / 8 = 1 atom from corners +1atom at body center, empirical formula = NiTi

c) Both have coordination numbers of 8 (both are surrounded by 8 atoms).

Step-by-step solution

Given Information

Nitinol is an alloy of nickel and titanium

Step: Concept Introduction

Cubic unit cell

The cubic unit cell is known as the smallest repeating unit, and it applies when all angles are$\mathbf{90}\mathbf{°}$nd all lengths are equal, with each axis being defined by a coordinate.

The simple cubic unit cell is denoted by eight atoms marked with the actual cube.

Body-centered cubic cell

Body-centered cubic (BCC) is the name given to a type of atom arrangement found in nature. A body-centered cubic unit cell structure consists of atoms arranged in a cube where each corner of the cube shares an atom and one atom positioned at the center.

Explanation

a) The unit cell consists of Ni at the cube corners and Ti at the body center or Ti at the cube corners and Ni at the body center.

b) 8 ×1 / 8 = 1 atom from corners +1 atom at body center, empirical formula = NiTi

c) Both have coordination numbers of 8 (both are surrounded by 8 atoms).