Spark and Herald of Ice

How do I make it work so that enemies get killed in frozen state and damage their surroundings? Just max crit chance for spark? Or is it more complicated than that?

I also see many spark users use controlled destruction which reduces crit by 100% and increases spell damage. Is it sensible to use that gem in combination with Herald of Ice?

Have you looked into Elemental Overload (keystone) and/or Call of the Brotherhood (unique ring)?

Thx for the hints, but I'm more interested how Herald of Ice cooperates with spark, because Herald of Ice is ice based and spark is lightning. Does that have negative effects on the status ailments produced by Herald of Ice? The amound of cold damage added to spells by Herald of Ice is rather low, and someone told me that status ailments depend on the damage size...?

There are a few ways to slice this cake

Controlled Destruction's penalty stacks additively with other increased critical strike chance stats you have, and it is pretty common to have over 800% increased critical strike chance, so CD usually cuts the DPS by rather less than 1/9 of 3/4s.

There is a Unique helmet that allows your Lightning Damage to Freeze, which will most likely help against tougher enemies like Rare monsters, bosses, durable Magics, and so on. It is called The Three Dragons.

On top of that, yes, Critical Strike Chance is the most popular way to inflict elemental status ailments. If you don't want to stack crit so high, there are some sources of "x% chance to freeze" you can access. For instance, there is a notable in the Templar start area that grants 5%, and Celestial Punishment to the left of Templar start area has another 5%.

One alternative to The Three Dragons is Call of the Brotherhood Unique ring. One or two of these can help your Spark have longer Freeze duration, which will increase your probability of killing a Frozen enemy. It may be annoying to split your damage between Lightning and Cold, though, depends on your build.

EDIT: added hyperlink to TTD