Sim Ulta Neou S Py Roe Le Ctri C and Dila Tom Etri C Stu Di Es of Pha Se Tra Nsiti on S in Tri Gly Ci Ne Sulp Hate a Nd Gl Yci Ne Posphite Crystals

Temp erature dependence s of the linear dimension L ( T ) and spontaneous polari zati on P s( T ) for tri glycine sulphate and glycine posphite single crystals have been measured in the same run of temp erature. A decrease in the spontaneous electrostriction coe£cient Q L of both crystals studied is displayed w hen approaching the corresp ondi ng phase transition point T c . A temp erature dep endence of the coe£cients Q L ( T ) show s that the rates of temp erature changes of displ acement of the atomic complexes of corresponding crystal structure forming the square of spontaneous polariz atio n P 2 s (primary order parameter ) and the displa cements of all atomic complexes forming the spontaneous linear thermal expansio n £ L s =L (secondary order parameter) are di ̃erent. T he applyin g external electric Ùeld E = 3 È 1 0 V /m to triglyci ne sulphate crystal does not inÛuence essentially the temp erature dep endence of Q L ( T ) in the temp erature range of phase transition b elow T c . PACS numb ers: 77.80.Bh