Monoclinic-orthorhombic phase transitions in A_2BX_4 single crystals with Sr_2GeS_4-type structure

Monoclinic-orthorhombic phase transitions in A_2BX_4 single crystals with Sr_2GeS_4-type structure

Creators Kasano H.

Creators Kojima M.

Creators Shouji T.

Creators Mashiyama H.

The structural phase transitions including the monoclinic-orthorhombic transition (α-β transition) in K_2ZnI_4, Rb_2CoI_4 and Rb_2MnI_4 are investigated by means of X-ray diffraction. These compounds take the Sr_2GeS_4-type structure at room temperature. In Rb_2CoI_4 and Rb_2MnI_4, the α-modification is transformed to the β-modification (β-K_2SO_4-type structure) at 515 K and 510 K, respectively. In the β-modification of Rb_2MnI_4, it is found that the transition from the normal phase (space group Pmcn) to incommensurate one (modulation along c^*) takes place at around 520 K. On the other hand, the α-β transition is not observed up to the melting point in K_2ZnI_4. We discuss the α-β transition on the basis of the ratio the ionic radius of A^+ to the average bond length B-X in tetrahedral BX_4^＜2-＞ ion. It is found that the compounds in this family are classified into three types by the ratio.

[ISSN]0015-0193

[NCID]AA00644949

info:doi/10.1080/00150199508217325

[isVersionOf] [URI]http://www.tandf.co.uk/journals/titles/00150193.asp