Pressure dependence of free-energy expansion coefficients inPbTiO3andBaTiO3

The Influence of Hydrostatic Pressure on Phase Transition in Ferroelectrics of Displacement Type

“…They, respectively, make up for BaTiO 3 : −48 K/GPa and +4,2 K/GPa 2 ; for SrTiO 3 : −17 K/GPa and +3,4 K/GPa 2 ; for PbTiO 3 : −71 K/GPa and +16 K/GPa 2 , for Sn 2 P 2 Se 6 : −178 K/GPa and −160 K/GPa 2 , for Sn 2 P 2 S 6 : −221 K/GPa and +139 K/GPa 2 ; for SbSJ: −371 K/GPa and +727 K/GPa 2 . The values of (∂T 0p /∂p) coefficient obtained for different crystals agree well with the results of direct experimental measurements [3][4][5][6]. The value of (∂ 2 T 0p /∂p 2 ) coefficient for all crystals except SbSJ are within the error of the experimental determination.…”

“…For the second case at the value of pressure that is assigned to extremuma in dependences C w (p) and α 0T (p) the inflection (∂ 2 T 0p /∂p 2 ) = 0 depending on T 0p (p) is observed. Taking into account that experimentally established [3][4][5][6] p,T -diagrams of ferroelectrics (except for SbSJ) have a linear character, it was of interest to estimate the value of non-linear pressure coefficient of PT temperature shift (∂ 2 T 0p /∂p 2 ) for different ferroelectrics. In accordance with these relationships using the results of works [3][4][5][6] the values of linear and quadratic PT shift temperature coefficients for different ferroelectrics are calculated.…”

“…Taking into account that experimentally established [3][4][5][6] p,T -diagrams of ferroelectrics (except for SbSJ) have a linear character, it was of interest to estimate the value of non-linear pressure coefficient of PT temperature shift (∂ 2 T 0p /∂p 2 ) for different ferroelectrics. In accordance with these relationships using the results of works [3][4][5][6] the values of linear and quadratic PT shift temperature coefficients for different ferroelectrics are calculated. They, respectively, make up for BaTiO 3 : −48 K/GPa and +4,2 K/GPa 2 ; for SrTiO 3 : −17 K/GPa and +3,4 K/GPa 2 ; for PbTiO 3 : −71 K/GPa and +16 K/GPa 2 , for Sn 2 P 2 Se 6 : −178 K/GPa and −160 K/GPa 2 , for Sn 2 P 2 S 6 : −221 K/GPa and +139 K/GPa 2 ; for SbSJ: −371 K/GPa and +727 K/GPa 2 .…”

“…In some works [1,2] within the phenomenological theory, the change in temperature and character of PT in ferroelectrics of displacement type at an all-sided compressibility has qualitatively been explained. However, at quantitative calculations of tricritical point coordinates and pressure coefficients of shift of PT temperatures for specific ferroelectric crystals, there takes place an essential discrepancy with experimental results [3][4][5][6]. It should be mentioned that the authors of these works do not pay attention to the experimentally known fact -Curie-Weiss constant pressure dependence.…”

“…In this caseβ is dependent on p only ifα non-linearly depends on p (that is h = 0). Taking into account that experimental dependences ε −1 (p) ∼ =α(p) for ferroelectrics of displacement type have a linear character [3][4][5][6] it becomes doubtful howβ coefficient may change with the pressure at h = 0. Secondly, α 0 as well as C w0 are independent of the pressure.…”