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The Behaviour of (NH 4 ) 2 Cd 2 (SO 4 ) 3 under Pressure
Author(s) -
Glogarová M.,
Frenzel C.,
Hegenbarth E.
Publication year - 1972
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220530139
Subject(s) - bar (unit) , electrostriction , phase transition , ferroelectricity , hydrostatic pressure , lattice (music) , materials science , condensed matter physics , triple point , homogeneous , thermodynamics , physics , dielectric , piezoelectricity , optoelectronics , meteorology , acoustics , composite material
The effect of hydrostatic pressure up to 1400 bar on (NH 4 ) 2 Cd 2 (SO 4 ) 3 from 300 to 20 °K was studied. For pressures up to 824 bar the shift of the ferroelectric phase transition temperature, T tr , was found ∂ T tr /∂ p = + 3.35 × 10 −3 deg/bar. The permittivity, ϵ, above T tr fulfilled ∂ϵ/∂ p < 0. These experimental results cannot be explained by the electrostrictive interaction only. This can be done, however, using the thermodynamic potential taking into account that the phase transition is caused by the instability in non‐homogeneous lattice vibration modes. For pressures higher than 824 bar two phase transitions occurred. It was found that ∂ T tr /∂ p = −0.62 × 10 −3 deg/bar and for the other transition ∂ T tr /∂ p = + 10.3 × 10 −3 deg/bar. At a pressure of 824 bar a triple point exists.