Is it like 平安 is used mainly when talking about the 平安時代 or in terms of historical peace?
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In the Balanced Corpus of Contemporary Written Japanese, we can see the following trend
In other words, 平安 seems to be primarily used as a reference to the Heian period.
It can be used to mean "calm" (as opposed to "peaceful" 平和), but for this purpose 平穏 is more common: