Amorphous: A glass, not having a crystalline structure.

Compressor: A machine used to increase the pressure of (compress) a gas.

Crystalline: Having each element's atoms bonded in a regular, repeating structure in space.

Hydrogen: The first element on the periodic table. Hydrogen is a flammable gas that is lighter than air and exists in its natural state as H₂.

Isotopes: Atoms of the same element with different numbers of neutrons in their nuclei.

Mechanical alloying: A method of alloying by ball milling (grinding and pulverizing) powder materials together.

Nanostructured: Having a size on the order of nanometers (10^-9 meters).

Nickel-cadmium cell: A storage battery having a positive electrode of nickel and a negative electrode of cadmium, widely used in cordless appliances. Without recharging, it can serve as a primary battery.