US EPA

1783920 

Journal Article 

Modelling phase changes in the potassium titanyl phosphate system 

Glasser, L; Catlow, CRA 

1997 

Yes 

Journal of Materials Chemistry
ISSN: 0959-9428
EISSN: 1364-5501 

7 

12 

2537-2542 

WOS:A1997YL60300039 

Potassium titanyl phosphate (KTiOPO4, KTP) is the principal
member of a group of isomorphous compounds, some of which have important non-linear optical
properties. These structures have the acentric space group symmetry Pna2(1) and are
ferroelectric. KTP itself undergoes a first-order, displacive isosymmetric phase change at 5.8
GPa at ambient temperature, as well as a second-order, displacive, order-disorder change to a
paraelectric phase, with space group Pnan, under ambient pressure at 934 degrees C. Eight of
these materials have been modelled using the static lattice modelling techniques in the GULP
code. The materials modelled are: potassium, thallium and rubidium titanyl phosphates; potassium
stannyl phosphate; potassium vanadyl phosphate; and potassium, rubidium and caesium titanyl
arsenates. The modelling of the effects of pressure (based on the ambient pressure structures
only) reproduces the isosymmetric phase change in KTP, and predicts similar pressure-driven phase
changes for seven of the eight structures; only CsTiOAsO4, fails to demonstrate this phase
change. Certain of the high pressure structures modelled are rotationally twinned relative to
their ambient pressure progenitor structures, in a manner in accord with suggestions in the
literature. It did not prove possible to model the temperature-driven phase change using a
static, ordered model; this problem is ascribed to disorder in the cation positions in the high-
temperature phase.