Raman scattering study of ferroelectric phase transition in ammonium sulphate

Raman spectra of a LiN(HxD1‐x)4SO4 mixed crystal

“…6 b ; 355 and 380 em-1, a t 126 K), and vanish with rise of temperature, far below the 111-11 PT. An analogous behaviour was observed in ammonium sulphate [18], which is structurally similar to LAS. Using data on 6LiKS04 and 7LiKS04 crystals [19], which (though hexagonal) are close to LAS in their struc- …”

Phase transition and temperature dependence of the molecular distortion of ions in ammonium sulphate

“…One may also note that these observations and inferences are also corroborated by recent studies. For example, Iqbal and Christoe (1976) and Hirabayashi and Abe (1980) have also observed that the phase transition in AS is accompanied by deformation of the SO',ion. Badr and Awad (1984) and Abe and Shibata (1977) have inferred that the SO:is responsible for the spontaneous polarisation and it plays a vital role in the process of transition.…”

“…Ammonium sulphate (AS) undergoes a peculiar ferroelectric phase transition (PT) at 223 K. The tetra-molecular unit cell of AS belongs to the Dii space group in the paraelectric phase and to CT, in the ferroelectric; it contains two crystallographically different ammonium ions: NH: (I) and NH: (11) (Wyckoff 1964, Schlemper andHamilton 1966). This transition has been the subject of a large number of studies: structural (Schlemper and Hamilton 1966), twin plane motion (Makita et a1 1976), dielectric (Ikeda et (Blinc and Levstek 1960), EPR (Abe and Shibata 1977, Barb et a1 1978, Manjunath and Srinivasan 1978, Ramnathan and Srinivasan 1978, Hirabayashi and Abe 1980, Narayana and Kevan 1381, DTA (Badr and Awad 1984) as well as IR absorption and Raman scattering (Torrie et a1 1972, Jain et a1 1973, Jain 1974, Petzelt et a1 1974, Venkateswarlu et a1 1975, Iqbal and Christoe 1976. Several semi-theoretical and theoretical studies of the transition are also available (Sawada et a1 1973, Jain andBist (1974a, b), Dvoiak and Ishibashi 1976, Onodera et a1 1978, Zinenko et a1 1980.…”

X-ray diffraction, thermal analysis, and Raman scattering study ofK2BeF4and comparison to other members of theSoláns1, González-Silgo2, Calvet3 et al. 1998Phys. Rev. B

“…This has been observed in the paraelectric-ferroelectric transition of ͑NH 4 ͒ 2 SO 4 . 17 The peak intensity of tr (K 1 ) shows the greatest temperature dependence, while the remaining peak intensities are constant. This is consistent with the assumption that the ion occupying site 1 is responsible for this transition in the ␤-K 2 SO 4 family of compounds.…”

“…The Raman spectrum of the ␤-K 2 SO 4 family of compounds has been studied from experimental results and from the semiempirical rigid-ion model. 14,17,18 In this, the spectrum is divided into two parts: the external mode spectrum below 400 cm Ϫ1 and the internal mode spectrum above this value. The two lowest frequency peaks are assigned to translational motion of K ions ͑there are two K ions with different coordination polyhedra in the crystal structure͒.…”