Phase Sequence of [CH3NH3]2CuCl4 Studied by X‐Ray Diffraction and Low‐Frequency Raman Scattering

The phase sequence of [CH3NH3]2CuCl4 was determined by X-ray structure analysis at T = 100, 297, and 363 K and temperature-dependent, low-frequency, Raman-scattering investigations were performed. At temperatures below Ttr = 348(2) K the structure is monoclinic, space group P21/a, lattice parameters a = 7.155(4) A, b = 7.424(4) A, c = 9.814(3) A, β = 109.18(7)° (for T = 100 K) and in the range 348 K < T < 455 K an orthorhombic high-temperature phase exists (space group Ccmb, lattice constants a = 7.34(2) A, b = 18.71(1) A, c = 7.33(5) A). The coexistence of two phases for low temperatures and the tetragonal high-temperature structure, reported previously for the title compound, are explained by twins and definitely discarded. Die Phasensequenz von [CH3NH3]2CuCl4 wurde mit Rontgenstrukturanalyse bei T = 100, 297 und 363 K bestimmt und temperaturabhangige Ramanmessungen im Niederfrequenzbereich durchgefuhrt. Fur Temperaturen unterhalb Ttr = 348(2) K hat die Struktur monokline Symmetrie, die Raumgruppe ist P21/a und die Gitterparameter betragen a = 7,155(4) A, b = 7,424(4) A, c = 9,814(3) A, β = 109,18(7)° (fur T = 100 K). Im Bereich 348 K < T < 455 K schliest sich eine orthorhombische Hochtemperaturphase an (Raumgruppe Ccmb, Gitterkonstanten a = 7,34(2) A, b = 18,71(1) A, c = 7,33(5) A). Die gleichzeitige Existenz von zwei Phasen im Tieftemperaturbereich und einer tetragonalen Hochtemperaturphase, die in fruheren Arbeiten beschrieben wurde, ist auf Verzwillingungen zuruckzufuhren.

[1]  N. Achiwa,et al.  Weak ferromagnetism of the layered perovskite (CnH2n+1NH3)2MnCl4 (n=1, 2 and 3) , 1990 .

[2]  W. Haije,et al.  A pseudo-Jahn-Teller effect, coupled with the E(X) epsilon Jahn-Teller effect , 1987 .

[3]  Y. Uemori,et al.  Phase transition and electrical properties of mono-, di-, tri- and tetraalkyl (or aryl) ammonium tetrahalogenocuprates(II) , 1984 .

[4]  J. Beneš,et al.  Second‐order phase transition of 1,4‐butanediyldiammonium manganese tetrachloride. A neutron diffraction study on clustered crystals , 1980 .

[5]  M. Couzi,et al.  Low‐frequency raman spectra and phase transitions in perovskite‐type layer compounds. (CH3NH3)2MnCl4 and (CH3NH3)CdCl4 , 1977 .

[6]  G. Chapuis,et al.  X-ray study of structural phase transitions in the perovskite-type layer compound (CH3NH3)2CdCl4 , 1976 .

[7]  K. Knorr,et al.  On the second‐order phase transition in (CH3NH3)2MnCl4. A single‐crystal neutron diffraction study at 404 and 293 K , 1975 .

[8]  G. Chapuis,et al.  X‐Ray study of the structural first‐order phase transition (Cmca‐P42/ncm) in (CH3NH3)2CdCl4 , 1975 .

[9]  K. Knorr,et al.  Birefringence, X-ray and neutron diffraction measurements on the structural phase transitions of (CH3NH3)2 MnCl4 and (CH3NH3)2FeCl4 , 1974 .

[10]  H. Remy,et al.  Über Chlorokomplexsalze des zweiwertigen Kupfers. , 1933 .

[11]  H. Fuess,,et al.  Crystal structure of monomethylammoniumtrichloromercurate(II) in the ferroelectric (neutron) and paraelectric phase , 1988 .

[12]  M. White,et al.  The Orthorhombic to Monoclinic Structural Phase-Transition in the Layer Compound Tetrachlorobis(Methylammonium) Copper-II, (CH3NH3)2CuCl4 , 1982 .

[13]  R. Blinc,et al.  13 C nuclear magnetic resonance study of phase transitions in a lipid bilayer embedded in a crystalline matrix: (C10H21NH3)2CdCl4 and (C10H21NH3)2CuCl4 , 1980 .

[14]  K. Nakamoto.  Infrared and Raman Spectra of Inorganic and Coordination Compounds , 1978 .