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'Phase transitions' in keywords Facet   Publication Year 1994  [X]
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1994[X]
1Author    Peter Remmert, Edmund Fischer, Hans-Ulrich HummelRequires cookie*
 Title    Phasenuntersuchungen im System 2 H a -T a S 2-2 H c -M o S 2 Investigations on Phases in the System 2 H a -T a S 2-2 H c -M o S 2  
 Abstract    Ternary phases in the system TaS2-M o S 2 have been obtained by thermal reactions at 1050 °C of binary layered disulfides and N H 4C1 as promotor. Ternary phases Taj_*Mo*S2 exist in the range 0.5 < jc< 0.9. In the range of 0.25 < * < 0.55 the reactions are quantitative and the phase-compositions are determined by the amounts of the starting materials. For x < 0 .2 lT -T a S 2 and for jc> 0.60 2 H c -M o S 2 are contaminating the resulting ternary phases. Ternary phases have been characterized by X-ray powder diffraction and are indexed rhombohedrally on the basis o f a 3 R-structure with metals in trigonal-prismatic coordination. The phases Tal jcMo*S2 with 0.25 < * < 0.55 show a reversible transition of higher order asso­ ciated with a change in the electrical conductivity mechanism. B elow 420 K the phases show semiconductivity while above 460 K metallic conductivity is observed. 
  Reference    Z. Naturforsch. 49b, 1175—1178 (1994); eingegangen am 15. April 1994 
  Published    1994 
  Keywords    Ternary Phases, Preparation, Phase Transition 
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 TEI-XML for    default:Reihe_B/49/ZNB-1994-49b-1175.pdf 
 Identifier    ZNB-1994-49b-1175 
 Volume    49 
2Author    Tsutomu Okuda, Yoshihiro Kinoshita, Hiromitsu Terao, Koji YamadaRequires cookie*
 Title    Structure and Bonding of Bromoantimonate (III) Complexes with Unusual Valency by Means of NQR and Powder X-Ray Diffraction  
 Abstract    NQR and powder X-ray diffraction were observed for several bromoantimonate (III) complexes which contain C"H2n+ jNF^ (n = 1 -3) or (C"H2lt + 1)2N H 2 (n = 1 -4) as a cation. The bond character, anion structure, crystal structure, and phase transition are discussed on the basis of the three-center-four-electron bond. A good correlation was found between the halogen NQR frequency and the Sb-X bond length. 
  Reference    Z. Naturforsch. 49a, 185—192 (1994); received July 23 1993 
  Published    1994 
  Keywords    81Br NQR, Temperature dependence, Phase transition, Crystal structure 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0185.pdf 
 Identifier    ZNA-1994-49a-0185 
 Volume    49 
3Author    Barbara Szafrańska, Zdzisław PająkRequires cookie*
 Title    Molecular Motion in Solid Tetraethyl-and Tetrabutylammonium Perchlorates  
 Abstract    The proton N M R second moment and spin-lattice relaxation time for polycrystalline tetraethyl-and tetrabutylammonium perchlorates have been measured over a wide range of temperatures. Solid-solid phase transitions related to the onset of cation tumbling were found for both compounds and confirmed by DSC. In the low temperature phases methyl-group reorientation was evidenced. For tetrabutylammonium cation a dynamic nonequivalence of one methyl group is found. The geared motion of the alkyl chains related with the onset of successive C H 2-group reorientations is suggested. 
  Reference    Z. Naturforsch. 49a, 465—468 (1994); received December 7 1993 
  Published    1994 
  Keywords    N M R, Molecular motions, Phase transitions 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0465.pdf 
 Identifier    ZNA-1994-49a-0465 
 Volume    49 
4Author    J. Zaleski, R. JakubasRequires cookie*
 Title    The Dielectric and Dilatometric Single Crystal Studies of Phase Transitions in a New Member of Family of Halogenoantimonates(III) [C(NH2)3l2SbCl5* [C(NH2)3]C1  
 Abstract    The results of dielectric, dilatometric and DSC studies on a new member of the family of alkylammonium halogenoantimonates ([(C(NH2)3]2SbCl5 • [(C(NH2)3]C1) are presented. This com­ pound undergoes three phase transitions at 146 K, 162 K, and 366 K. The two low temperature transitions are suggested to be of the displacive type and the high temperature one of the order-dis-order type. The character of temperature changes of the electric permittivity at the lowest temper­ ature transition suggest a polar phase below the transition temperature. 
  Reference    Z. Naturforsch. 49a, 709—713 (1994); received March 23 1994 
  Published    1994 
  Keywords    Phase transitions, Dielectric, Dilatometric, Halogenoantimonate, Guanidinium 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0709.pdf 
 Identifier    ZNA-1994-49a-0709 
 Volume    49 
5Author    Jacek ZaleskiRequires cookie*
 Title    Crystal Structure and Phase Transitions of [C(NH2)3]3Sb2C l9 * 0.9 H 20 A dam Pietraszko  
 Abstract    The room temperature structure of [C(NH2)3]3Sb2C l9 ■ 0.9 H 20 (GNCA) was solved. It crystal­ lizes in the monoclinic C2/c space group with a = 15.275, b = 8.794, c = 17.904 (in Ä), ß = 96.40°, V = 2390 Ä 3, Z = 4. Refinement of the atomic parameters by a least squares methods gave R = 0.042, wR = 0.039 for 1958 reflections with F>4ct(F). The structure consists of polyanionic (Sb2Cl|_)n layers built of deformed corner connected SbX^-octahedra. Two crystallographically inequivalent guanidinium cations are present, one situated between polyanionic layers, the other one together with a disordered water molecule inside cavities formed by polyanions. Temperature X-ray scattering experiments together with DSC studies were carried out above room temperature. Temperature dependence of the lattice parameters between 300 K and 380 K was determined and a phase transition of mixed order at 364 K was revealed. 
  Reference    Z. Naturforsch. 49a, 895—901 (1994); received June 7 1994 
  Published    1994 
  Keywords    Guanidinium, Chloroantimonate, Crystal structure, Phase transition, DSC 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0895.pdf 
 Identifier    ZNA-1994-49a-0895 
 Volume    49 
6Author    Günter RadonsRequires cookie*
 Title    Mechanisms for Phase Transitions in the Multifractal Analysis of Invariant Densities of Correlated Random Maps  
 Abstract    Multifractal properties of the invariant densities of correlated random maps are analyzed. It is proven that within the thermodynamical formalism phase transitions for finite correlations may be due to transients. For systems with infinite correlations we show analytically that phase transitions can occur as a consequence of localization-delocalization transitions of relevant eigenfunctions. 
  Reference    Z. Naturforsch. 49a, 1219—1222 (1994); received October 12 1994 
  Published    1994 
  Keywords    Fractals, Dynamical systems, Phase transitions, Stochastic automata, Random walk 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-1219.pdf 
 Identifier    ZNA-1994-49a-1219 
 Volume    49 
7Author    Motoko Kenmotsu, Hisashi Honda, Hiroshi Ohki, Ryuichi Ikeda, Tomoki Erata, Akira Tasaki, Yoshihiro FurukawaRequires cookie*
 Title    Ionic Dynamics in Plastic Crystal KNOz Studied by 39K and I5NNMR  
 Abstract    The spin-lattice relaxation time of 39K N M R observed in the low-temperature phase (T <264.1 K) of K N 0 2 is explained by the quadrupole mechanism contributed from a newly found N O J m otion. The in-plane C 3 reorientation and the overvall N 0 2 rotation as well as the self-diffusion were shown in the intermediate phase (T < 314.7 K) and the high-temperature plastic phase (T < melting point: 710 K), respectively, by observing 39K and 15N N M R relaxation times and 1SN lineshapes. 
  Reference    Z. Naturforsch. 49a, 247 (1994); received July 23 1993 
  Published    1994 
  Keywords    K e y words: Solid NM R, Q uadrupole relaxation, Plastic crystal, Phase transition, Chemical shift anisotropy 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0247.pdf 
 Identifier    ZNA-1994-49a-0247 
 Volume    49 
8Author    Tetsuo Asaji, Hideshi Tomizawa, Ryuichi IkedaRequires cookie*
 Title    Structural Phase Transition of N,N-Dimethylnitramine as Studied by 14N Nuclear Quadrupole Resonance  
 Abstract    The 14N nuclear quadrupole relaxation time and resonance frequencies v+, v_, and vd of N,N-dimethylnitramine were measured between 14 and 313 K. The frequency increase of v+ and v_ observed below Tc (108 K) is explained by the increase o f prc electrons in the am ino nitrogen caused by the deformation of the m olecular skelton, which is planar above Tc. The sharp Tip minima for v+ and v_ observed at Tc are attributed to the softening o f vibration modes on both sides of Tc. The fluctuation o f the nitrogen-hydrogen m agnetic dipolar interaction due to C H 3 reorientation was detected as a broad T'lQ minimum observed around 84 K. A logarithmic divergence of Tu31 observed on the high-temperature side o f Tc suggests the presence o f a diffusive or overdamped-type soft mode. 
  Reference    Z. Naturforsch. 49a, 253 (1994); received August 10 1993 
  Published    1994 
  Keywords    M olecular crystal, Phase transition, Soft mode, NQ R, Spin-lattice relaxation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0253.pdf 
 Identifier    ZNA-1994-49a-0253 
 Volume    49 
9Author    K. Yamada, K. Isobe, T. Okuda, Y. FurukawaRequires cookie*
 Title    Successive Phase Transitions and High Ionic Conductivity of Trichlorogermanate (II) Salts as Studied by 35C1 NQR and Powder X-Ray Diffraction  
 Abstract    A series o f trichlorogermanate(II) salts (AG eCl3, A = Rb, Cs, C H 3N H 3, and (C H 3)4N) have been synthesized and characterized by 35C1 N Q R , 35C1 N M R , AC conductivity, DTA, and X-ray diffrac­ tion techniques. In the temperature range studied two, two, five, and four phases were confirmed for the Rb, Cs, C H 3N H 3, and (C H 3)4N salts, respectively. From the 35C1 N Q R and structural data, isolated pyramidal G eC l3 anions were recognized in the low temperature phases. With increasing temperature the relaxation times of the 35C1 N Q R decreased exponentially and the signals disap­ peared far below the melting point. This suggests that the reorientation of the anion about the pseudo three-fold axis is excited. With further increase in temperature, the ionic conductivity of C H 3N H 3G eC l3 and (C H 3)4N G eC l3 increased drastically at the phase transitions to their cubic perovskite phases (C H 3N H 3G eC l3: a = 10-1 S m -1 at 400 K, (C H 3)4N G eC l3: a = 5 x 10-2 S m _1 at 420 K). The mobile ion was confirmed to be the chloride ion by means of 35C1 N M R and X-ray diffraction. 
  Reference    Z. Naturforsch. 49a, 258 (1994); received July 23 1993 
  Published    1994 
  Keywords    35C1 N Q R, 35C1 N M R, Ionic conductivity, Rietveld analysis, Phase transition 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0258.pdf 
 Identifier    ZNA-1994-49a-0258 
 Volume    49 
10Author    Hirokazu Nakayama, Taro Eguchi, Nobuo NakamuraRequires cookie*
 Title    Phase Transitions in 4,4'-Dichlorobenzophenone as Studied by 3SC1FT-NQR  
 Abstract    The temperature dependence of 35C1 N Q R frequencies in 4,4'-dichlorobenzophenone was m ea­ sured between 9.3 and 372 K by the pulse Fourier-transform method. Successive phase transitions were observed at 189 and 194 K. Concerning these phase transitions, the curious thermal hysteresis phenom enon found in a previous N Q R experiment was not reproduced in the present study. It also follow s that N Q R indicates another phase transition around 220 K, although no thermal anom aly was detected there by DTA. Tentative explanations for these three phase transitions are presented in relation to the incommensurability between 189 and 220 K. In addition, a novel phase transition was found to occur at 331 K according to both DTA and 35C1 N Q R. A single N Q R line observed at room temperature splits into two com ponents above 331 K, suggesting that the symmetry above 331 K is lower than that at room temperature. This is the behavior o f re-entrant phase transition, and it reveals the quasi-continuous nature. 
  Reference    Z. Naturforsch. 49a, 267 (1994); received August 21 1993 
  Published    1994 
  Keywords    35C1 N Q R, 4, 4'-dichlorobenzophenone, Phase transition, Incomm ensurate phase 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0267.pdf 
 Identifier    ZNA-1994-49a-0267 
 Volume    49 
11Author    Y. Kume, T. A. Sajia, R. IkedaRequires cookie*
 Title    Low Temperature Isotope Effect in Ammonium Hexachloroselenate(IV) Studied by 35C1 NQR  
 Abstract    The temperature dependence o f the 35C1 N Q R frequency and spin-lattice relaxation time TlQ of (N H 4)2SeCl6 and (N D 4)2SeCl6 were measured from 400 K to 24.8 and 53.8 K, respectively. The disappearance of N Q R signals in the low temperature region of both salts is attributed to phase transitions. We concluded from the temperature behavior of just above the transition point that the operative mechanism o f the transition is different in these salts: The transition of (N D 4)2SeCl6 seems to be associated with rotary soft modes, while in the natural salt non-rotary soft modes seem to play an important role at the transition. 
  Reference    Z. Naturforsch. 49a, 297 (1994); received August 13 1993 
  Published    1994 
  Keywords    Isotope effect, Spin-lattice relaxation, N Q R, Phase transition, Ammonium hexa­ chloroselenate, Deuterated am m onium hexachloroselenate 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0297.pdf 
 Identifier    ZNA-1994-49a-0297 
 Volume    49