OK.
Firstly lightning.
Have you ever seen lightning from a cloudless, blue sky?
Of course not. Lightning is associated with clouds. Heavy thick clouds.
Clouds are created by thermal evaporation of water from land and sea.
They are moved around in the atmosphere by thermally generated air currents.
As they move around they bump into each other and rub shoulders and whatnot.
This action (and maybe some of the other more esoteric ideas in Wikipedia too) cause electrons to be rubbed from one cloud mass and transferred to another so the whole cloud mass becomes charged. Eventually this charge is discharged by the flash and ground return stroke we see as lightning, although sometimes the flashes also pass between oppositely charged clouds, if they approach each other closely enough.
Note that electrons are transferred.
This is why I say the process is thermally driven.
Now for piezoelectricity.
This phenomenon occurs in neutral (non charged) solids. For certain solids if they are strained (distorted) the direction of the ionic bonds is changed slightly. This polarises the crystal as whole so that one end becomes positve and the other negative. The crystal remains neutral overall, however. The faster the straining the greater the voltage developed this way, which is why spark igniters incorporate a hammer mechanism.
There is an dual phenomenon known as electrostriction where the crystal changes shape in response to an applied voltage.
go well
