Yup. 'Refractory' is the word you want; a thin-set mortar is fine; ideally you want it to be rated for over 2400 F, but something that can handle about 2000 will do if that's all you can find locally.
We often use fire clay (refractory clay) instead of chemical-set mortars; it's easy to work with, and doesn't damage the brick if something needs to get taken apart later (like to replace a cracked brick).
You can use ordinary concrete and cement mortars in the casing (outer 3-4") of the heater, just not in the firebox area.
If you do use Portland
cement products, be sure there is a good expansion joint (a layer of flexible insulation or something like that) between firebox and surface masonry, so the firebox doesn't crack the concrete when it expands with heat. Earthen masonry is a lot easier to patch than cracked concrete; and it's also possible for the force to be relieved inward in ways that screw up your firebox.