Phase transitions in NH₄LiSO₄ and (NH₄)₃Li(SO₄)₂

ABSTRACT

We review recent understanding of the crystallographic phases and its relation to ferroelectricity in ammonium lithium sulphate (NH₄LiSO₄) using the crystal structural data reported before and present our recent idea about its ferroelectricity. In this paper, we also report phase transitions and crystal structure at room temperature of tori-ammonium lithium di-sulphate ((NH₄)₃Li(SO₄)₂) from our recent experimental results. NH₄LiSO₄ which is one of the (NH₄)₂SO₄ family ferroelectrics and (NH₄)₃Li(SO₄)₂ which is one of the A₃B(XY₄)₂-type derived from the ABXY₄-type were crystallized by evaporating the aqueous solution at room temperature. The phase transition and crystal structure were studied by means of thermogravimetric analysis, differential scanning calorimetry and single-crystal X-ray diffraction. In addition, phase transitions and ferroelectricity of NH₄LiSO₄ will be discussed from the crystal structural changes.