Ferroelectric-paraelectric phase transitions with no group-supergroup relation between the space groups of both phases?

The structures Of Sr-3(FeF6)(2), beta -NbO2, TlBO2 and CrOF3, previously re ported as possible ferroelectrics with no group-supergroup relation between the ferroelectric and the paraelectric symmetries, have been carefully stu died. We could not confirm any structural pseudosymmetry with respect to a space group which is not a supergroup of their room- temperature polar spac e group. In all cases, pseudosymmetry was indeed detected, but only for non polar supergroups of the actual space groups of the structures. In this sen se., the four compounds are possible ferroelectrics. but fulfilling the usu al group-supergroup relation between the phase symmetries.