scholarly journals Role of NH4 ions in successive phase transitions of perovskite type (NH4)2ZnX4 (X = Cl, Br) by 1H MAS NMR and 14N NMR

RSC Advances ◽  
2018 ◽  
Vol 8 (21) ◽  
pp. 11316-11323 ◽  
Author(s):  
Ae Ran Lim
Keyword(s):  
Phase Transitions ◽  
Chemical Shifts ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
1H Mas Nmr ◽  
Spin Lattice ◽  
Successive Phase ◽  
Perovskite Type

The 1H chemical shifts and the spin-lattice relaxation time, T1ρ, in the rotating frame of (NH4)2ZnX4 (X = Cl, Br) are observed in order to investigate local phenomena related to successive phase transitions.

Successive Phase Transitions in Potassium Hexachloroselenate(IV) Revealed by 35Cl NQR

1996 ◽  
Vol 51 (5-6) ◽  
pp. 705-709 ◽  
Author(s):  
Tetsuo Asaji ◽  
Masaki Ohkawa ◽  
Takehiko Chiba ◽  
Makoto Kaga
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Structural Phase Transitions ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Successive Phase

Abstract K2SeCl6 undergoes structural phase transitions of first order at 35 K, 65 K, and 79 K. The temperature dependence of the 35Cl NQR spin-lattice relaxation time suggests that the phase transitions at 65 K and 79 K are displacive ones associated with a resonant soft mode. The presence of a precursor cluster is suggested by the temperature dependence of the signal intensity above 79 K.

Incommensurability and Domain Structure of K2SbF5

2002 ◽  
Vol 57 (6-7) ◽  
pp. 456-460
Author(s):  
A. M. Panich ◽  
L. A. Zemnukhova ◽  
R. L. Davidovich
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Relaxation Measurements ◽  
Increasing Temperature

Phase transitions and incommensurability in K2SbF5 have been studied by means of 123Sb NQR spectra and spin-lattice relaxation measurements. The phase transitions occur at 117, 135 and 260 K. The line shape and temperature dependence of the spin-lattice relaxation time T1 at 135 to 260 K are characteristic for an incommensurate state with a plane wave modulation regime. At 117 to 135 K a distinct fine structure of the NQR spectra has been observed. The X-ray diffraction pattern of this phase is interpreted as a coexistence of two modulation waves along the a and b axis with wave vectors (a*/6 + b*/6) and (a*/2 + b*/2), respectively. The best interpretation that fits our NQR data is a coexistence of two domains, the structures of which are modulated with different periods in such a manner that each domain exhibits only one of the aforementioned modulation waves. Redistribution of line intensities with the variation of temperature shows that one of the domains becomes energetically preferable on cooling and is transformed into the low temperature phase at 117 K. The 123SbNQR measurements in K2SbF5 show unusually short values of T1, which become close to the spin-spin relaxation time T2 with increasing temperature. - Pacs: 61.44.Fw, 64.60, 64.70, 64.70.Rh, 76.60

Chemical shifts for compounds of the group IV elements silicon and tin

1968 ◽  
Vol 46 (8) ◽  
pp. 1399-1414 ◽  
Author(s):  
B. K. Hunter ◽  
L. W. Reeves
Keyword(s):  
Chemical Shift ◽  
Complex Formation ◽  
Chemical Shifts ◽  
Equilibrium Constants ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Shielding Effect ◽  
Spin Lattice ◽  
Group Iv Elements

Chemical shifts for 29Si in seven series of molecules of the type XnSiY4−n have been measured where Y is an alkyl group and X varies widely in electronegativity. A considerable amount of proton and fluorine chemical shift data has been obtained for the same compounds and in one series (CH3)nSiCl4−n the 13C chemical shifts in the methyl groups have been measured.The gross features of the 29Si chemical shifts are understood by considering the series (Alkyl)3SiX with the electronegativity of X widely varied. The hybridization at silicon is approximately conserved in these series and the theoretically anticipated linear dependence on electronegativity of X is demonstrated. The ligands X = O, N, and F are exceptional and these 29Si chemical shifts have a high field shift. This additional shielding has been associated with (p → d)π bonding. The approximate nature of present chemical shift theories is not likely to provide a measure of the order of (p → d)π bonding.The 29Si chemical shifts in the series XnSiY4−n are discussed and also indicate a net shielding effect with (p → d)π bonding. A comparison is always made with corresponding 13C chemical shifts. A long range proton–proton coupling in molecules Me3SnX and Me2SnX2, H—C—Si—C—H, is observed when and only when X = O, (N?), F.119Sn chemical shifts in a series of alkyltin compounds have been measured. The same dependence on the electronegativity of X in the series (Alkyl)3SnX is noted, but the variation of X is much more limited. Some shielding due to (p → d)π bonding in the series (n-Butyl)nSnCl4−n is suggested. The tin chemical shift has been measured as a function of concentration and solvent for simple methyltin bromides and chlorides. In donor solvents, it has been possible to obtain equilibrium constants for complex formation from tin dilution chemical shifts. The nature of the bonding in complexes suggested previously is consistent with the variations in the coupling constant |JSn–C–H| with concentration. The distinction between ionization and complex formation with the solvent for (CH3)2SnCl2 can be made on the basis of the concentration dependence of |JSn–C–H|The spin–lattice relaxation time T1for 13C and 29Si in natural abundance in several pure degassed compounds has been measured. These are not in the case of 13C (as has been suggested) of the order several minutes, but are always less than 50 s and in one case as low as 3–4 s. Both 29Si and 13C T1 values follow what might be expected on the basis of a dipole–dipole mechanism from the closest protons. The short value of 35 s in CS2 is probably a result of spin–rotation interaction in the liquid state.

Spectroscopic and differential scanning calorimetric studies of the phase transitions in oxanorbornane

1998 ◽  
Vol 76 (10) ◽  
pp. 1365-1370 ◽  
Author(s):  
Ralph M Paroli ◽  
Denis FR Gilson ◽  
Ian S Butler
Keyword(s):  
Phase Transitions ◽  
Group Analysis ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Factor Group ◽  
Spin Lattice Relaxation ◽  
Differential Scanning Calorimetric ◽  
Spin Lattice ◽  
Calorimetric Studies

Oxanorbornane (7-oxabicyclo[2.2.1]heptane, C6H10O) resembles other bicycloheptane-like molecules by exhibiting order-disorder transitions in the solid state. Differential scanning calorimetric studies show that five different phases may occur, with hysteresis in the transition temperatures. The vibrational spectra have been examined, and a factor group analysis of the vibrational splittings indicates that the crystal structure of the ordered phase has D2d symmetry. Activation energies for molecular motions were derived from proton spin-lattice relaxation time measurements.Key words: oxanorbornane, order-disorder, phase transitions.

NMR Study of Cation Motions in Ferroic [C(NH2)3]3Bi2Br9

2000 ◽  
Vol 55 (6-7) ◽  
pp. 570-574 ◽  
Author(s):  
M. Grottel ◽  
Z. Paja̡ka ◽  
R. Jakubasb
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Wide Temperature Range ◽  
Proton Nmr ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Potential Barriers ◽  
Spin Lattice ◽  
Nmr Study

The proton NMR second moment and spin-lattice relaxation time of polycrystalline [C(NH2)3]3Bi2Br9 were studied in a wide-temperature range. Dynamical inequivalence of two crystallographically different guanidinium cations has been revealed . The C3 reorientation of the two types of cations was found to be hindered by different potential barriers (25.1 kJ/mol and 34.7 kJ/mol). At higher temperatures an overall reorientation of the cations was revealed. The existence and order-disorder character of the phase transitions at 333, 350, 415, and 425 K have been confirmed.

Structural Phase Transitions and Ionic Motions in Pyridinium Hexachlorotellurate(IV),Hexachlorostannate(IV), and Hexabromostannate(IV) Crystals as Studied by 1H NMR

1989 ◽  
Vol 44 (4) ◽  
pp. 300-306 ◽  
Author(s):  
Yutaka Tai ◽  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr

Abstract The 1H NMR second moment M2 and the spin-lattice relaxation time T1 are determined for pyridinium hexachlorotellurate(IV), hexachlorostannate(IV), and hexabromostannate(IV) at various temperatures above ca. 140 K. The phase transition temperatures already reported from halogen NQR experiments are determined as 272, 331, and 285 K, respectively, by differential thermal analysis (DTA). The DTA as well as differential scanning calorimetry measurements show that the above phase transitions are of second-order. For pyridinium hexachlorotellurate(IV) and hexa-bromostannate(I V), a sharp 1H T1 dip was observed at the transition temperature. This is interpreted in terms of a phenomenon related to the critical fluctuation of an order parameter. From the measurements of 1H M2, 60° two-site jumps (60° flips) around the pseudo C6 axis of the cation are suggested to occur in the high temperature phases of the complexes. Modulation of X...1H (X = CI, Br) magnetic dipolar interactions due to the reorientational motion of the complex anions is considered as a possible relaxation mechanism in the high temperature phases.

Structure and Successive Phase Transitions of RGeBr3 (R = Alkylammonium) Studied by Means of NQR

1996 ◽  
Vol 51 (5-6) ◽  
pp. 686-692 ◽  
Author(s):  
Shusaku Gotou ◽  
Tsutomu Okuda ◽  
Toshirou Takahashi ◽  
Hiromitsu Terao ◽  
Koji Yamada
Keyword(s):  
Phase Transitions ◽  
Crystal Structures ◽  
Conduction Mechanism ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Rietveld Analysis ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Successive Phase

Abstract A series of tribromogermanate(II) complexes RGeBr3 (R = CH3NH3, (CH3)2NH2, (CH3)4N, C2H5NH3, (C2H5)4N) have been synthesized and characterized by 81Br NQR, AC conductivity, DTA, and X-rax diffraction. These measurements revealed the presence of successive phase transitions in these complexes. The crystal structures of Phases I and II in (NH3)4NGeBr3 were derived from the Rietveld analysis of powder X-ray diffraction. The electric conductivity was considerably high in CH3NH3GeBr3 and (NH3)4NGeBr3. The conduction mechanism is discussed on the basis of 81Br NQR spin-lattice relaxation times and crystal structures.

Low Temperature Isotope Effect in Ammonium Hexachloroselenate(IV) Studied by 35Cl NQR

1994 ◽  
Vol 49 (1-2) ◽  
pp. 297-301 ◽  
Author(s):  
Y. Kume ◽  
T. Asaji ◽  
R. Ikeda
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Low Temperature ◽  
Transition Point ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Soft Modes ◽  
35Cl Nqr

Abstract The temperature dependence o f the 35Cl NQR frequency and spin-lattice relaxation time T1Q of (NH4)2SeCl6 and (ND4)2SeCl6 were measured from 400 K to 24.8 and 53.8 K, respectively. The disappearance of NQR 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 (ND4)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.

Carbon-13 NMR and Raman Scattering Studies of Potassium Propoxybenzoate and Potassium Butoxybenzoate. Conformational Change Due to Micellization

1981 ◽  
Vol 36 (12) ◽  
pp. 1352-1356
Author(s):  
Hirofumi Okabayashi ◽  
Tadayoshi Yoshida ◽  
Yukimasa Terada ◽  
Teruki Ikeda ◽  
Kazuhiro Matsushita
Keyword(s):  
Conformational Change ◽  
Chemical Shifts ◽  
Deuterium Oxide ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Alkoxy Group ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Methylene Groups

Abstract Carbon-13 NMR chemical shifts and carbon-13 spin-lattice relaxation times of potassium propoxybenzoate and potassium butoxybenzoate in deuterium oxide solution were measured at various concentrations. For the alkoxy group, the earbon-13 resonance peak of the O-CH2 segment is shifted rapidly up-field upon micellization, while the resonance peaks of other methylene groups are shifted downfield. This observation is ascribed to the conformational change of the alkoxy group on micellization. In the monomolecular solution of potassium butoxybenzoate, the restricted state of the O-CH2 bond was estimated by carbon-13 spin-lattice relaxation time measurement. It was also found that micellization brings about a further restricted internal rotation about the O-CH2 bond.

Sign in / Sign up

Export Citation Format

Share Document