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1996 (1)
1995 (1)
1992 (1)
1Author    Hirokazu Nakayama, Taro Eguchi, Michihiko KishitaRequires cookie*
 Title    Phase Transitions in Bis(4-chlorophenyl)sulfone as Studied by 35 C1 FT-NQR  
 Abstract    The temperature dependence of 35 C1 NQR frequencies in bis(4-chlorophenyl)sulfone was mea-sured in the temperature range of 4.2-297 K. Below 115 K four NQR lines due to four inequivalent chlorines exist in the commensurate phase, contrary to the single NQR line reported by Corbero et al. It follows that the commensurate-incommensurate transition is of the first-order, and the incommensurate-normal transition at 150 K is quasi-continuous. It is also suggested that the succes-sive phase transitions are triggered by the small angle rotation of the molecules about their C2-axes. 
  Reference    Z. Naturforsch. 47a, 232—236 (1992); received July 10 1991 
  Published    1992 
  Keywords    35 C1 NQR, Bis(4-chlorophenyl)sulfone, 'H NMR, Incommensurate phase, Phase tran-sition 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0232.pdf 
 Identifier    ZNA-1992-47a-0232 
 Volume    47 
2Author    U. Häcker3, D. Michel3, K.-P Hölzer, J. PeterssonbRequires cookie*
 Title    2H a n d 14N N M  
 Abstract    R S tu d ie s o f th e D y n a m ic s in th e I n c o m m e n s u r a te P h a s e s o f B e ta in e C a lc iu m c h lo rid e D ih y d r a te Dedicated to Professor Dr. W . Müller-Warmuth on the occasion of his 65th birthday 2H and 14N NMR spin-lattice relaxation rates were measured in the structurally incommensu-rately (IC) modulated phases of deuterated and undeuterated betaine calciumchloride dihydrate, respectively. The results are related to the elementary excitations of these phases. The presence of low-frequency phase fluctuations of the modulation wave leads to higher spin-lattice relaxation rates compared with the high-temperature normal phase and the commensurate (C) phases. The corre­ sponding "phason" contributions are found to be nearly constant in the whole IC phases. In the IC phases near the transitions to the C phases the relaxation rates decrease due to the formation of the soliton lattice. This interpretation is in agreement with the results of previous dielectric measure­ ments. 
  Reference    Z. Naturforsch. 50a, 368—372 (1995); received November 8 1994 
  Published    1995 
  Keywords    Nuclear-spin-lattice relaxation, Betaine calciumchloride dihydrate, Incommensurate phases, Phason modes, Incommensurate-commensurate phase transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0368.pdf 
 Identifier    ZNA-1995-50a-0368 
 Volume    50 
3Author    R. K. Subramanian, S.Uma Maheswari, K. Venu, V.S S SastryRequires cookie*
 Title    NQR Investigation of Anion Dynamics in Rb 2 Zn(Cl 1 _ x Br x ) 4  
 Abstract    The structural stability of Rb 2 Zn(Cl : -^Br^ (x = 1% and 3%) is investigated using the 35 C1 quadrupole resonance frequency and spin lattice relaxation time (T\q) in the paraelectric (PE) phase. The PE to incommensurate (IC) phase transition temperature 7", observed at 302 K in the pure compound, is lowered to 300 K for x = 1 % and to 293 K for x = 3%. These effects are smaller than in the earlier reported case of 3% Cs substitution in Rb 2 ZnCl 4 , which reduces T x by 25 K. While bigger cation substitution affects only the barrier for anion dynamics about directions perpendicular to the a-axis (direction of low temperature IC modulation wave), bigger anion substitution is found to affect the barrier for anion dynamics about the a-axis as well. The present study also indicates that the cusp like dip in 71 q observed while approaching T x from above (characterizing the soft mode condensation associated with the structural phase transition) is essentially unaffected by anion impurity substitution, in contrast to the case where bigger cation substitution tends to smear the transitional effects. These results seem to suggest the dominant role played by cations in stabilizing the PE phase of these A 2 BX 4 systems, in comparison to anions. 
  Reference    Z. Naturforsch. 51a, 745—750 (1996); received January 30 1996 
  Published    1996 
  Keywords    NQR, A 2 BX 4 systems, Anion dynamics, Structural stability, Incommensurate phases 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0745.pdf 
 Identifier    ZNA-1996-51a-0745 
 Volume    51