Phase transitions in KTP isostructures: correlation between structure and Tc in germanium-doped RbTiOPO4

• Published in: Acta crystallographica. Section B, Structural science Structural science, 2003-10, Vol.59 (5), p.588-595
• Main Authors: Norberg, Stefan T., Gustafsson, Joacim, Mellander, Bengt-Erik
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Dielectric, piezoelectric, ferroelectric and antiferroelectric materials; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Exact sciences and technology; Inorganic compounds; Kdp- and tgs-type crystals; KTP isostructures; phase transitions; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768103018688

Crystals of germanium‐doped rubidium titanyl phosphate, Rb2(Ti)(Ge0.121Ti0.879)O2(PO4)2 (GeRTP#1) and Rb2(Ge0.125­Ti0.875)(Ge0.225Ti0.775)O2(PO4)2 (GeRTP#2), have been structurally characterized from X‐ray diffraction data at room temperature. In addition, a third structure, Rb2(TiO)2(PO4)2 (RTP), has been reinvestigated. The exchange of titanium for germanium results in a less distorted octahedral coordination around the two crystallographically independent titanium sites. Additionally, rubidium split‐cation positions have been found in these doped RTP crystals. Dielectric measurements show that the phase‐transition temperature, Tc, decreases with increasing germanium concentration, and a direct correlation between the room‐temperature split of the rubidium cations and Tc has been discovered. General trends regarding the relationship between the room‐temperature structures of KTP‐like compounds and their Tc values are discussed.