MM'PO4, a new family of ferroic compounds

The two phosphates CsCoPO4 and CsZnPO4 are each shown to undergo two different phase transitions when heated above room temperature. The first one—form class 2 to presumably class 2 mm—is a ferroelastic to paraelastic transition, whereas the second one, occurring at a higher temperature—presumably from class 2 mm to class mmm—exhibit a weak dielectric character. This paper is a first account on the ferroelastic and dielectric properties of these compounds which are otherwise shown to be two particular members of a wide family of ferroic compounds of the general formula M+ M'2+ PO4 or M+ M'2+ AsO4 where M is a monovalent metal and M' a divalent metal with a tetrahedral coordination.