An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Permittivity and ac conductivity study of the layered perovskite [(CH3)(C6H5)3P]2MnCl4 showing evidence of phase transition
Physics Letters A, 1999
Abstract The permittivity and ac conductivity of the compound bis(methyltriphenylphosphonium)2tet... more Abstract The permittivity and ac conductivity of the compound bis(methyltriphenylphosphonium)2tetrachloro-manganate(II) have been measured in the temperature range 300–400 K and in the frequency range 0.1–20 kHz . Differential thermal analysis reveals structural phase transition in the temperature range 365 K 1 kHz) and the conductivity results. The conductivity follows the Arrhenius relation with different activation energies and conduction mechanisms: region (I) → 345±3 K region (II) → 365±3 K region (III) → 372±2 K region (IV) with activation energies ΔE1∼10 meV, ΔE2∼1–0.2 eV and ΔE4∼2–1 eV for temperature regions (I), (II) and (IV), respectively. In region (I) extrinsic type conduction prevails. Analysis of the experimental data based on the jump relaxation model, showed that translation motion of the proton and reorientation hopping between equivalent sites of the metal chloride anion and the phenyl groups are responsible for the observed ac conductivity in the temperature region (II). In region (IV) overlap large polarons predominates .
Irreversibility line of an Ag-doped Hg-based superconductor
Superconductor Science and Technology, 2010
The effect of doping with Ag of the bulk superconducting Hg0.3La0.7Ba2Ca3(Cu1 − xAgx)4O10 + δ, 0.... more The effect of doping with Ag of the bulk superconducting Hg0.3La0.7Ba2Ca3(Cu1 − xAgx)4O10 + δ, 0.1 ≤ x ≤ 0.3 phase (Hg-1234) is presented. The lattice parameter a = 3.824 Å remains constant, while parameter c was found to increase from c = 19.0225 Å (x = 0.0) to 19.08 Å (x = 0.3) with the addition of Ag. The variation of Tc versus the c-parameter exhibits a cupola-shaped behavior. The irreversibility line is thermally activated. The logarithmic plot of Hirr versus (1 − Tirr/Tc(0)) shows a crossover temperature reflecting a transition from two- to three-dimensional behavior with increasing temperature. Fitting of the results to different models is discussed. Thermally activated de-pinning according to Matsushita’s formula gives the best fit.
Conduction mechanisms in the magnetic insulator [(CH 3 ) 2 NH 2 ] 2 CoCl 4
Phase Transitions, 2005
Magnetic susceptibility in the temperature range 170–370 K and ac permittivity and conductivity i... more Magnetic susceptibility in the temperature range 170–370 K and ac permittivity and conductivity in the frequency range 5 Hz–1 kHz over the same temperature range for the compound [(CH3)2NH2]2CoCl4 were carried out. The results indicate three phase transitions at Tc 1 = 245 ± 3 K, Tc 2 = 290 ± 5 K and Tc 3 = 320 ± 6 K. At T ≥ 290 K the paramagnetic compound conducts via band type mechanism with band gap = 2.42 eV. At lower temperatures correlated barrier hopping mechanism prevails, with an activation energy = 0.52 ± 0.04 eV, an effective barrier height = 0.73 eV and a hopping distance = 36.5 Å.
Differential thermal scanning of the new lipid-like bilayer material (CH2)io(NH3)2CdCl4 showed tw... more Differential thermal scanning of the new lipid-like bilayer material (CH2)io(NH3)2CdCl4 showed two structural phase transitions, with onset temperatures at T2 = (359 ± 2) K and 7, = (415± 1) K. Permittiv ity measurements were performed between room temperature and 450 K at 60-100 kHz. A step-like rise in permittivity at T2, associated with an order-disorder transition, is attributed to chain melting. Two anomalies at (413 ± 1) K and (430 ± 3) K, showing thermal hysteresis of-8 and 10 K, respectively, in dicate first order transitions which are associated with crystalline phase change. The AC conductivity follows an Arrhenius-type relation with the activation energy A£ varying with the frequency / according to the relation AE = A£0 [1-exp where AE0,f0 and a are 0.95 eV, 52 Hz and 0.11, respectively. The frequency dependent conductivity follows the power law a= C 7dc + ßcov, with 0.3 <s < 1.5 for hopping conduction of hydrogen and/or chloride ions in the high temperature range, and localized hopping and/or orientational motion predominating temperatures lower than 413 K. Variations of B and s with temperature are discussed.
The magnetic susceptibility of (C,,H2n ÷INH3)2FeCI4, where n = 1, 2, 3, 4 and [(CHa)2NH2]2FeC14, ... more The magnetic susceptibility of (C,,H2n ÷INH3)2FeCI4, where n = 1, 2, 3, 4 and [(CHa)2NH2]2FeC14, is measured in the temperature range 80-300 K. The results are interpreted in terms of a canted 2-dimensional antiferromagnet that approximates the X-Y model. The effect of varying the magnetic field strength on the susceptibility behaviour is discussed.
The synthesis and characterization of a new series of mono-, di-, and trinuclear Cr(II) borohydri... more The synthesis and characterization of a new series of mono-, di-, and trinuclear Cr(II) borohydride compounds is described. The reaction of CrCl2(TMEDA) with two equivalents of NaBH4 afforded the thermally unstable (TMEDA)Cr(BH4)2 (1), which was converted by treatment with pyridine into the octahedral monomeric (Py)4Cr(BH4)2 (2). The reaction proceeds via formation of an intermediate trinuclear complex {[(TMEDA)(Py)Cr(η2-BH4)]2[(Py)2Cr(η2-BH4)2]}(µ,η1-BH4)2 (3), which was isolated and characterized by X-ray crystallography. Reaction of 1 and 2 with both CO2 and RN=C=NR (R = Cy, iPr) afforded hydride insertion and formation of the corresponding diamagnetic lantern-type Cr(II) formate (HCO2)4Cr2Py2 (4) and formamidinate compounds [RNC(H)NR]2Cr2(µ-BH)4 (R = Cy (5a), iPr (5b)), respectively, with supershort Cr—Cr quadruple bonds. The structures of 1, 2, 3, and 5b were elucidated by X-ray analysis. Crystal data are as follows. 1: C6H24N2B2Cr, monoclinic, Cc, a = 8.517(2) Å, b = 15.921(5)...
The dielectric permittivity of the layered magnetic insulators [(CH2)3(NH3)2Cu1−xCdxCl4] with x=0... more The dielectric permittivity of the layered magnetic insulators [(CH2)3(NH3)2Cu1−xCdxCl4] with x=0, 0.3, 0.6, and 1 has been studied in the temperature range 300 K- 470 K at different frequencies. Single crystal- and powder-measurements for x = 0 revealed a ferroelectric phase transition at (434± 2) K. The ferroelectric Cu crystal and the antiferroelectric Cd salt were found to form solid solutions in the range 0.3 < x < 0.6. The permittivity results of samples with x = 0.3 and 0.6 showed the broad permittivity-temperature plateau typical of dielectric relaxors. The two samples follow the relationship 1/ε −1/εm =(T −Tm)γ /C, with γ =1.75 and 1.71 and C =4.13·105 K and 1.19·105 K for x = 0.3 and x = 0.6 samples, respectively. Anomalous change in the temperature variation of the permittivity (δε' /δ T) for the x = 1 sample at T ~ 374 K is ascribed to a structural phase transition. Thermal analysis for the x = 0 sample reveals two phase changes at T1 = 434.4 K and T2 = 334.5 K...
Electric and magnetic study of the new biodegradable complexes bis-(cyclopentanonyl-2,5DI(p-aminobenzylidine)MCl4, M = Mn 2, Co 2 and Cu 2
Phase Transitions, 2001
ABSTRACT The permittivity and AC conductivity in the temperature range 290 K- 460 K, in the frequ... more ABSTRACT The permittivity and AC conductivity in the temperature range 290 K- 460 K, in the frequency range 5.0 Hz-4.0 kHz, magnetic susceptibility over the temperature range 80K-460K, at different magnetic fields as well as x-ray diffraction and IR spectra have been measured for the biodegradable materials [A]2MCl4, in which A is cyclopentan-onyl-2,5-di(p-aminobenzylidine) and M = Mn, Co and Cu . X-ray analysis indicated that the materials crystallize in orthorhombic unit cell of dimensions a = 15.41(1) Å, b= 16.77(1) Å, c= 19.38(1) Å, a= 15.75(1) Å, b= 16.95(1) Å, c= 19.56(1) Å and a = 15.89(l)Å, b = 17.53(l)Å, c = 20.01(2)Å for the Mn +, Co and Cu materials, respectively. Electric and magnetic results indicate the following structural phase transitions: The conductivity follows Arrhenius relation. Near room temperature the activation energies are small and have nearly the same value (ΔEa∼170meV) for the three materials. At the high temperature phase, ΔE1 is frequency dependent and follows the relationship ΔE = ΔE0 [1 - exp - (f0/f)] with Eo varies from 1.2eV (Mn) to 2.88 eV (Cu).The frequency dependence of conductivity follows the universal power law [sgrave]∼ B(T)ω(T) Variation of s(T) and In B(T) with temperature shows discontinuities at the phase transitions. At high temperatures, phase (I), band type conduction prevails
Differential thermal analysis at high temperatures shows three endothermic peaks characterizing f... more Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T 1 = 313±2 K, T 2 = 320±4 K and T 3 = 360±1 K. The structural instability detected via the temperature dependence of permittivity at T 1 is ascribed to order-disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K-375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model.
The magnetic susceptibility of ((CH,),CHNH,),CuCl, is measured in the temperature range 340 to 78... more The magnetic susceptibility of ((CH,),CHNH,),CuCl, is measured in the temperature range 340 to 78 K. The susceptibility changes abruptly near the thermochromic temperature of 66 "C. The compound obeys the Curie-Weiss behaviour at high temperatures, but seems to behave like a two-dimensional ferromegnet at lower temperatures. A good fit between experimental and theoretical results is obtained using a Heisenberg ferromagnetic simple quadratic lattice model, t h k yields a J / K = 12.5. Die magnetkche Suszeptibilitiit von ((CH,),CHNH,),CuCl, wird im Temperaturbereich von 340 bis 78 K gemessen. Die Suszeptibiht iindert sich sprunghaft in der Niihe der thermochromen Temperatur von 56 "C. Die Verbindung befolgt das Curie-Weiss-Verhalten bei hohen Temperaturen, jedoch scheint sie sich bei tieferen Temperaturen wie ein zweidimensionaler Ferromagnet zu verhalten. Es wird eine gute Anpassung zwischen experimentellen und theoretischen Ergebnissen mit einem einfachen, quadratischen Gittermodell eines Heisenberg-Ferromagneten erhalten, wobei sich JIK = 12,6 ergibt.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Permittivity and ac conductivity study of the layered perovskite [(CH3)(C6H5)3P]2MnCl4 showing evidence of phase transition
Physics Letters A, 1999
Abstract The permittivity and ac conductivity of the compound bis(methyltriphenylphosphonium)2tet... more Abstract The permittivity and ac conductivity of the compound bis(methyltriphenylphosphonium)2tetrachloro-manganate(II) have been measured in the temperature range 300–400 K and in the frequency range 0.1–20 kHz . Differential thermal analysis reveals structural phase transition in the temperature range 365 K 1 kHz) and the conductivity results. The conductivity follows the Arrhenius relation with different activation energies and conduction mechanisms: region (I) → 345±3 K region (II) → 365±3 K region (III) → 372±2 K region (IV) with activation energies ΔE1∼10 meV, ΔE2∼1–0.2 eV and ΔE4∼2–1 eV for temperature regions (I), (II) and (IV), respectively. In region (I) extrinsic type conduction prevails. Analysis of the experimental data based on the jump relaxation model, showed that translation motion of the proton and reorientation hopping between equivalent sites of the metal chloride anion and the phenyl groups are responsible for the observed ac conductivity in the temperature region (II). In region (IV) overlap large polarons predominates .
Irreversibility line of an Ag-doped Hg-based superconductor
Superconductor Science and Technology, 2010
The effect of doping with Ag of the bulk superconducting Hg0.3La0.7Ba2Ca3(Cu1 − xAgx)4O10 + δ, 0.... more The effect of doping with Ag of the bulk superconducting Hg0.3La0.7Ba2Ca3(Cu1 − xAgx)4O10 + δ, 0.1 ≤ x ≤ 0.3 phase (Hg-1234) is presented. The lattice parameter a = 3.824 Å remains constant, while parameter c was found to increase from c = 19.0225 Å (x = 0.0) to 19.08 Å (x = 0.3) with the addition of Ag. The variation of Tc versus the c-parameter exhibits a cupola-shaped behavior. The irreversibility line is thermally activated. The logarithmic plot of Hirr versus (1 − Tirr/Tc(0)) shows a crossover temperature reflecting a transition from two- to three-dimensional behavior with increasing temperature. Fitting of the results to different models is discussed. Thermally activated de-pinning according to Matsushita’s formula gives the best fit.
Conduction mechanisms in the magnetic insulator [(CH 3 ) 2 NH 2 ] 2 CoCl 4
Phase Transitions, 2005
Magnetic susceptibility in the temperature range 170–370 K and ac permittivity and conductivity i... more Magnetic susceptibility in the temperature range 170–370 K and ac permittivity and conductivity in the frequency range 5 Hz–1 kHz over the same temperature range for the compound [(CH3)2NH2]2CoCl4 were carried out. The results indicate three phase transitions at Tc 1 = 245 ± 3 K, Tc 2 = 290 ± 5 K and Tc 3 = 320 ± 6 K. At T ≥ 290 K the paramagnetic compound conducts via band type mechanism with band gap = 2.42 eV. At lower temperatures correlated barrier hopping mechanism prevails, with an activation energy = 0.52 ± 0.04 eV, an effective barrier height = 0.73 eV and a hopping distance = 36.5 Å.
Differential thermal scanning of the new lipid-like bilayer material (CH2)io(NH3)2CdCl4 showed tw... more Differential thermal scanning of the new lipid-like bilayer material (CH2)io(NH3)2CdCl4 showed two structural phase transitions, with onset temperatures at T2 = (359 ± 2) K and 7, = (415± 1) K. Permittiv ity measurements were performed between room temperature and 450 K at 60-100 kHz. A step-like rise in permittivity at T2, associated with an order-disorder transition, is attributed to chain melting. Two anomalies at (413 ± 1) K and (430 ± 3) K, showing thermal hysteresis of-8 and 10 K, respectively, in dicate first order transitions which are associated with crystalline phase change. The AC conductivity follows an Arrhenius-type relation with the activation energy A£ varying with the frequency / according to the relation AE = A£0 [1-exp where AE0,f0 and a are 0.95 eV, 52 Hz and 0.11, respectively. The frequency dependent conductivity follows the power law a= C 7dc + ßcov, with 0.3 <s < 1.5 for hopping conduction of hydrogen and/or chloride ions in the high temperature range, and localized hopping and/or orientational motion predominating temperatures lower than 413 K. Variations of B and s with temperature are discussed.
The magnetic susceptibility of (C,,H2n ÷INH3)2FeCI4, where n = 1, 2, 3, 4 and [(CHa)2NH2]2FeC14, ... more The magnetic susceptibility of (C,,H2n ÷INH3)2FeCI4, where n = 1, 2, 3, 4 and [(CHa)2NH2]2FeC14, is measured in the temperature range 80-300 K. The results are interpreted in terms of a canted 2-dimensional antiferromagnet that approximates the X-Y model. The effect of varying the magnetic field strength on the susceptibility behaviour is discussed.
The synthesis and characterization of a new series of mono-, di-, and trinuclear Cr(II) borohydri... more The synthesis and characterization of a new series of mono-, di-, and trinuclear Cr(II) borohydride compounds is described. The reaction of CrCl2(TMEDA) with two equivalents of NaBH4 afforded the thermally unstable (TMEDA)Cr(BH4)2 (1), which was converted by treatment with pyridine into the octahedral monomeric (Py)4Cr(BH4)2 (2). The reaction proceeds via formation of an intermediate trinuclear complex {[(TMEDA)(Py)Cr(η2-BH4)]2[(Py)2Cr(η2-BH4)2]}(µ,η1-BH4)2 (3), which was isolated and characterized by X-ray crystallography. Reaction of 1 and 2 with both CO2 and RN=C=NR (R = Cy, iPr) afforded hydride insertion and formation of the corresponding diamagnetic lantern-type Cr(II) formate (HCO2)4Cr2Py2 (4) and formamidinate compounds [RNC(H)NR]2Cr2(µ-BH)4 (R = Cy (5a), iPr (5b)), respectively, with supershort Cr—Cr quadruple bonds. The structures of 1, 2, 3, and 5b were elucidated by X-ray analysis. Crystal data are as follows. 1: C6H24N2B2Cr, monoclinic, Cc, a = 8.517(2) Å, b = 15.921(5)...
The dielectric permittivity of the layered magnetic insulators [(CH2)3(NH3)2Cu1−xCdxCl4] with x=0... more The dielectric permittivity of the layered magnetic insulators [(CH2)3(NH3)2Cu1−xCdxCl4] with x=0, 0.3, 0.6, and 1 has been studied in the temperature range 300 K- 470 K at different frequencies. Single crystal- and powder-measurements for x = 0 revealed a ferroelectric phase transition at (434± 2) K. The ferroelectric Cu crystal and the antiferroelectric Cd salt were found to form solid solutions in the range 0.3 < x < 0.6. The permittivity results of samples with x = 0.3 and 0.6 showed the broad permittivity-temperature plateau typical of dielectric relaxors. The two samples follow the relationship 1/ε −1/εm =(T −Tm)γ /C, with γ =1.75 and 1.71 and C =4.13·105 K and 1.19·105 K for x = 0.3 and x = 0.6 samples, respectively. Anomalous change in the temperature variation of the permittivity (δε' /δ T) for the x = 1 sample at T ~ 374 K is ascribed to a structural phase transition. Thermal analysis for the x = 0 sample reveals two phase changes at T1 = 434.4 K and T2 = 334.5 K...
Electric and magnetic study of the new biodegradable complexes bis-(cyclopentanonyl-2,5DI(p-aminobenzylidine)MCl4, M = Mn 2, Co 2 and Cu 2
Phase Transitions, 2001
ABSTRACT The permittivity and AC conductivity in the temperature range 290 K- 460 K, in the frequ... more ABSTRACT The permittivity and AC conductivity in the temperature range 290 K- 460 K, in the frequency range 5.0 Hz-4.0 kHz, magnetic susceptibility over the temperature range 80K-460K, at different magnetic fields as well as x-ray diffraction and IR spectra have been measured for the biodegradable materials [A]2MCl4, in which A is cyclopentan-onyl-2,5-di(p-aminobenzylidine) and M = Mn, Co and Cu . X-ray analysis indicated that the materials crystallize in orthorhombic unit cell of dimensions a = 15.41(1) Å, b= 16.77(1) Å, c= 19.38(1) Å, a= 15.75(1) Å, b= 16.95(1) Å, c= 19.56(1) Å and a = 15.89(l)Å, b = 17.53(l)Å, c = 20.01(2)Å for the Mn +, Co and Cu materials, respectively. Electric and magnetic results indicate the following structural phase transitions: The conductivity follows Arrhenius relation. Near room temperature the activation energies are small and have nearly the same value (ΔEa∼170meV) for the three materials. At the high temperature phase, ΔE1 is frequency dependent and follows the relationship ΔE = ΔE0 [1 - exp - (f0/f)] with Eo varies from 1.2eV (Mn) to 2.88 eV (Cu).The frequency dependence of conductivity follows the universal power law [sgrave]∼ B(T)ω(T) Variation of s(T) and In B(T) with temperature shows discontinuities at the phase transitions. At high temperatures, phase (I), band type conduction prevails
Differential thermal analysis at high temperatures shows three endothermic peaks characterizing f... more Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T 1 = 313±2 K, T 2 = 320±4 K and T 3 = 360±1 K. The structural instability detected via the temperature dependence of permittivity at T 1 is ascribed to order-disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K-375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model.
The magnetic susceptibility of ((CH,),CHNH,),CuCl, is measured in the temperature range 340 to 78... more The magnetic susceptibility of ((CH,),CHNH,),CuCl, is measured in the temperature range 340 to 78 K. The susceptibility changes abruptly near the thermochromic temperature of 66 "C. The compound obeys the Curie-Weiss behaviour at high temperatures, but seems to behave like a two-dimensional ferromegnet at lower temperatures. A good fit between experimental and theoretical results is obtained using a Heisenberg ferromagnetic simple quadratic lattice model, t h k yields a J / K = 12.5. Die magnetkche Suszeptibilitiit von ((CH,),CHNH,),CuCl, wird im Temperaturbereich von 340 bis 78 K gemessen. Die Suszeptibiht iindert sich sprunghaft in der Niihe der thermochromen Temperatur von 56 "C. Die Verbindung befolgt das Curie-Weiss-Verhalten bei hohen Temperaturen, jedoch scheint sie sich bei tieferen Temperaturen wie ein zweidimensionaler Ferromagnet zu verhalten. Es wird eine gute Anpassung zwischen experimentellen und theoretischen Ergebnissen mit einem einfachen, quadratischen Gittermodell eines Heisenberg-Ferromagneten erhalten, wobei sich JIK = 12,6 ergibt.
Uploads
Papers by Mohga Mostafa