85 research outputs found
Thermal properties of polycrystalline : crystal structure and phase transitions
The X-ray powder diffraction (XRPD) pattern
of [Mn(NH
3
)
6
](ClO
4
)
2
at room temperature can be indexed
in the regular (cubic) system (Fm
3m space group) with
lattice cell parameter
a
=
11.5729 A
̊
and with four mole-
cules per unit cell. The XRPD pattern at 100 K is evidently
different, and it indicates lowering of the crystal structure.
One phase transition at
T
h
C1
=
143.5 K (on heating) and at
T
c
C1
=
137.6 K (on cooling) was detected by DSC for
[Mn(NH
3
)
6
](ClO
4
)
2
in the range of 120–300 K. The fol-
lowing thermodynamic parameters for phase I
$
phase II
transition were obtained:
D
H
=
3.1
±
0.2 kJ mol
-
1
and
D
S
=
21.6
±
0.3 J mol
-
1
K
-
1
. The large value of entropy
changes (
D
S
) indicates considerable configurational disor-
der in the high temperature phase. The presence of 5.9 K
hysteresis of the phase transition temperature at
T
C
and
sharpness of the heat flow anomaly attest that the detected
phase transition is of the first-order type. Appearing of the
two new bands (splitting of
d
s
(HNH)
F
1u
mode) in FT-MIR
spectra at the vicinity of 1200 cm
-
1
suggests that the phase
transition undergoes a change of the crystal structure
Thermal properties of studied by adiabatic and relaxation calorimetry
Four (solid–solid) phase transitions were detected in the temperature range of (9 to 300) K in polycrystalline [Cr(NH3)6](BF4)3 at TC1 = 240.7 K, TC2 = 108.0 K, TC3 = 91.9 K, and TC4 = 61.3 K by adiabatic calorimetry. The measurements by relaxation calorimetry were followed on lowering temperature from 20 K down to 0.35 K under six different external magnetic field values (9, 7, 5, 3, 1 and 0) T. For non-zero values of applied magnetic field well-defined Schottky anomaly appears. Magnetic heat capacity was calculated assuming the zero-field splitting for the decoupled Cr(III) ions. There is no discrepancy between the observed and calculated values. Isothermal magnetization curve recorded up to 5 T was measured at temperature of 1.8 K
IINS, FT-IR and DFT study of the internal dynamics of [4-apyH][]
A combination of infrared and inelastic incoherent neutron scattering spectroscopies with the density functional theory and semi-empirical calculations was applied to propose an assignment of the vibrational spectra of 4-aminopyridine chloroantimonate(IV)
- …