Properties of a cathode used in thermionic valves.

•  It should have a low work function. A low work function helps to emit electrons from the cathode surface in a comparatively lower temperature
• It should have a high melting point. The temperature required to emit an electron from the cathode surface is quite high compared to the melting point of normal metals. A lower melting point causes vaporization of metals before they emit electrons.
  
• It should have high mechanical strength.