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The reconstructive structural transitions result in two classes of the surface phase transitions at sufficient high temperatures: disordering and melting.

I think the reflections that occurred at lower temperatures were because the material crystallized at that temperature. It is not necessarily an artifact, like the reflections that occur in water, and additional reflections appear when we freeze it. That is, the structural structure of the atoms of the substance varies depending on the temperature

You can run XRD with an empty sample holder to exclude artifacts from the chamber and sample holder. if it will not help then peaks are from your sample:)

I believe reflexes at low temperatures compared to room temperature do not necessarily indicate artifacts. It could be attributed to real physical phenomena like Order-Disorder Transitions, structural changes, etc.