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1.
In this study we introduce the spectroscopic modifications of Pippard relations and apply them to the disorder-induced Raman modes of NH4Cl in the first-order (P=0) and second-order (2.8 kbar) phase regions in this crystalline system. We obtain linear variations of the specific heat CP with our observed frequency shifts [(1/ν)(∂ν/∂T)P] of those Raman modes studied for the first-order and second-order phase transitions in NH4Cl. This will be discussed in detail. 相似文献
2.
Yurtseven H Yanik A Sen S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(1):105-109
We establish here a linear variation of the specific heat C(P) with the frequency shifts (1/nu)( partial differentialnu/ partial differentialT)(P) close to the lambda-phase transition in NH(4)Br (T(lambda)=234K). This linear relationship is based on our spectroscopically modified Pippard relations. For this verification of our relations, we use our observed Raman frequencies of the lattice mode of nu(7) (56cm(-1)) and the internal mode of nu(2) (1684cm(-1)) in the NH(4)Br crystalline system. Our study given here indicates that the thermodynamic data can be obtained from the measured frequencies. 相似文献
3.
The molar volume of solid and liquid benzene was calculated at various pressures (at constant temperatures), and the Pippard relations were examined close to the melting point in this organic molecule.The molar volume calculated is in good agreement with the observed data, which decreases as the pressure increases up to about 150 MPa. The Pippard relations are also valid within this pressure range at constant temperatures studied here for the solid and liquid phases of benzene. 相似文献
4.
Richard J. Goff 《Journal of solid state chemistry》2009,182(10):2626-2631
The relaxor ferroelectric Pb2Bi4Ti5O18 has been studied by Rietveld refinement of powder neutron diffraction data collected at temperatures of 100, 250 and 400 °C. Our refinements are compatible with the ‘average’ crystal structure of Pb2Bi4Ti5O18 undergoing the phase transition sequence F2mm→I4mm→I4/mmm as a function of increasing temperature, with the latter phase being observed above the known ferroelectric Curie temperature, Tm, and the intermediate phase consistent with a previously observed dielectric anomaly around 207 °C. The results are, however, in conflict with both observation of a symmetry lowering (to space group B2eb) in the lowest temperature phase, observed by electron diffraction, and also with electrical property measurements, which suggest both a- and c-axis polarisation up to Tm. Nevertheless, these crystallographic results are consistent with the observation of relaxor behaviour in this material, and underline the importance of considering ‘long-range’ versus ‘local’ structural effects in relaxor materials. 相似文献
5.
Tari O Yurtseven H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(8):1615-1621
We establish in this study a linear variation of the specific heat Cp with the frequency shifts (l/v)(delta v/delta T) in the sinusoidal antiferroelectric phase of NaNO2, according to the first Pippard relation which we have modified spectroscopically. For this linear relationship we use the Brillouin frequencies of acoustic phonon modes for the q[010], q[001] and q[100] modes of NaNO2 in the sinusoidal antiferroelectric phase. We then calculate dT/dP values due to those modes studied for NaNO2, which agree with the literature values. 相似文献
6.
The crystal structure of the Aurivillius phase Bi5TiNbWO15 has been analyzed in detail using powder X-ray and neutron diffraction. The structure can be described as a regular intergrowth of alternating single and double perovskite-like layers sandwiched between fluorite-like bismuth oxide layers, such that the layer sequence is … [WO4]-[Bi2O2]-[BiTiNbO7]-[Bi2O2] …. There is complete ordering of tungsten within the B sites of the single perovskite layer, so that the structure can be described as a direct intergrowth of the ‘component’ Aurivillius phases Bi2WO6 and Bi3TiNbO9. At 25 °C the structure adopts the polar orthorhombic space group I2cm, , , . 相似文献
7.
Of the various EPR spectra observed in the ferroelectric phase of NaNO2, a spectrum designated as spectrum II is observed to have some peculiar properties like dependence of its intensity on growth conditions of the crystal, its disappearance below ≈60°C after heat treatment of the crystal, its reappearance by heating above ≈60°C and also by application of an external dc electric field at ≈30°C. These observations suggest the possible existence, around Mn2+-vacancy complex in the ferroelectric phase of NaNO2, of a metastable structure intermediate to the paraelectric and ferroelectric phase structures. 相似文献
8.
Computer modelling techniques have been used to investigate the defect and oxygen transport properties of the Aurivillius phase Bi4Ti3O12. A range of cation dopant substitutions has been considered including the incorporation of trivalent ions (M3+=Al, Ga and In). The substitution of In3+ onto the Bi site in the [Bi2O2] layer is predicted to be the most favourable. The calculations suggest that lanthanide (Ln3+) doping at the dilute limit preferentially occurs in the [Bi2O2] layer, with probable distribution over both the [Bi2O2] and the perovskite A-site at higher dopant levels. It is predicted that the reduction process involving Ti3+ and oxygen vacancy formation is energetically favourable. The energetics of oxide vacancy migration between various oxygen sites in the structure have been investigated. 相似文献
9.
Transparent glasses of various compositions in the system (100−x)Li2B4O7−x(SrO-Bi2O3-Nb2O5) (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi2Nb2O9 phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple-Didomemenico and Gladstone-Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active. 相似文献
10.
S. F. Solodovnikov B. G. Bazarov E. Yu. Badmaeva Yu. L. Tushinova E. S. Zolotova Zh. G. Bazarova 《Journal of Structural Chemistry》2004,45(4):657-662
Phase relations have been studied for the subsolidus region of the Dy2O3-HfO2-MoO3 system; binary molybdates, Dy2Hf(MoO4)5 and Dy2Hf2(MoO4)7, were found to form. The crystal structure of the latter has been solved (a = 20.661(3) , b = 9.816(1) , c = 13.796(3) , = 113.47(1)°, Z = 4, space group C2/c, R = 0.023) and found to be a new type of structure. In the structure, MoO4 tetrahedra are linked by their vertices with HfO6 octahedra and DyO8 tetragonal antiprisms to form a 3D open-work, in which one can isolate double-row tetrahedral and octahedral chains extended down the c axis.Original Russian Text Copyright © 2004 by S. F. Solodovnikov, B. G. Bazarov, E. Yu. Badmaeva, Yu. L. Tushinova, E. S. Zolotova, and Zh. G. BazarovaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 692–697, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
11.
The equilibrium phase relations for the CaOIrO2Ir system were determined in air using the quenching technique. The system contains three stable compounds 4CaO·IrO2, 2CaO·IrO2, and CaO·IrO2; they dissociate to an oxide phase, Ir metal, and oxygen at 1240, 1170, and 1135°C, respectively. A metastable form of CaO·IrO2 occurs at temperatures between 900 and 1100°C. Indexed X-ray diffraction powder patterns of all compounds are given. 相似文献
12.
V.V. Politaev V.B. Nalbandyan B.S. Medvedev E.S. Shvetsova 《Journal of solid state chemistry》2007,180(3):1045-1050
Phase relations in the MnO-SiO2-Li4SiO4 subsystem have been investigated by X-ray diffraction after solid-state reactions in hydrogen at 950-1150 °C. Both cation-deficient and cation-excess solid solutions Li2+2xMn1−xSiO4 (−0.2?x?0.2) based on Li2MnSiO4 have been found. According to Rietveld analysis, Li2MnSiO4 (monoclinic, P21/n, a=6.3368(1), b=10.9146(2), c=5.0730(1) Å, β=90.987(1)°) is isostructural with γII-Li2ZnSiO4 and low-temperature Li2MgSiO4. All components are in tetrahedral environment, (MnSiO4)2− framework is built of four-, six- and eight-member rings of tetrahedra. Testing Li2MnSiO4 in an electrochemical cell showed that only 4% Li could be extracted between 3.5 and 5 V against Li metal. These results are discussed in comparison with those for recently reported orthorhombic layered Li2MnSiO4 and other tetrahedral Li2MXO4 phases. 相似文献
13.
Subsolidus phase relation studies in the NaSb3O7-Na3SbO4-CuO-CuSb2O6 quadrangle of Na2O-CuO-Sb2On system at 1123-1173 K revealed the formation of one new compound Na3Cu2SbO6. It is a superstructure derived from α-NaFeO2 type, space group C2/m, lattice constants: a=5.6759(1) Å, b=8.8659(1) Å, c=5.8379(1) Å, β=113.289(1)°. All ions are in octahedral environment, but CuO6 polyhedron exhibits strong elongation due to Jahn-Teller effect (Cu-O: 2.000(2) Å×2, 2.021(2) Å×2, 2.494(3) Å×2), whereas SbO6 octahedron is almost regular. The relationship to other similar superlattices is discussed. 相似文献
14.
Brendan J. Kennedy Qingdi Zhou Maxim Avdeev 《Journal of solid state chemistry》2011,184(11):2987-2993
The synthesis of bulk samples of polycrystalline CdTiO3 in both the rhombohedral ilmenite and orthorhombic perovskite forms is described and the structures of these have been refined using powder neutron diffraction data. This involved the preparation of samples enriched in 114Cd. Cooling perovskite-type CdTiO3 to 4 K induces a ferroelectric phase transition, with the neutron data suggesting the low temperature structure is in Pna21. Mode analysis shows the polar mode to be dominant at low temperatures. The ilmenite-structure of CdTiO3 is compared with that of ZnTiO3. The refined scattering length of the 114Cd is estimated to be 5.56 fm. Attempts to dope CdTiO3 with Ca and Sr are described. 相似文献
15.
The electric field gradients (EFG) at the sites of the cations and the “central” atoms of the anions in the ionic crystals NaNO2, NaBF4, NaNO3 and Ba(NO3)2 are calculated by a method based on a combination of the semi-empirical INDO method for the charge distribution and the intramolecular EFG with a lattice summation in the framework of the extended multipole model. At some lattice sites the contribution of the induced dipole and quadrupole moments to the EFG is comparable with the contribution of the point charges. The charge distribution within the molecular ions is found by adjusting either the calculated asymmetry parameter η or the z-component of the EFG to the experimental value deduced from nuclear quadrupole coupling constants. These charge distributions are in good agreement with those gained from INDO calculations. The calculated and experimental quadrupole coupling constants of nuclei in anions and cations are compared. 相似文献
16.
Ba6Ti17O40, Ba4Ti13O30, BaTi4O9, and Ba2Ti9O20 are the only compounds which were found to have a stability range in the subsolidus of the BaTiO3TiO2 system. BaTi2O5 and BaTi5O11, reported in other studies, apparently are not stable. The compound reported as Ba2Ti5O12 appears to have been mistaken for Ba6Ti17O40. X-Ray diffraction powder data are given for this phase which is monoclinic with a = 9.890, b = 17.117, c = 18.933 Å and β=98°42.6′. The phase formulated previously as BaTi3O7 is shown to be Ba4Ti13O30 based on structural and density considerations, phase equilibria, and single crystal and powder X-ray diffraction data. This compound is orthorhombic with a = 17.072, b = 9.862, and c = 14.059 Å, probable space group, Cmca. An idealized structure for this phase is proposed. Ba2Ti9O20 decomposes above 1300°C in the solid state to BaTi4O9 plus rutile. Single crystals were grown using BaF2 as a mineralizer. 相似文献
17.
The decomposition of basic copper carbonate in the presence and absence of NaNO3–KNO3 eutectic melt has been studied by employing isothermal TG and dynamic TG/DSC techniques. The rate constants for the decomposition in the presence of eutectic melt were found to be higher than when carbonate was heated alone. In both the cases copper oxide was found to be the end product. Catalytic activity of copper oxide obtained by the two methods were tested for the decomposition of ammonium perchlorate. 相似文献
18.
The high-pressure phase diagram of CsD2PO4 to 4.5 GPa and temperatures between 0 and 470°C is reported. Comparisons are made with CsH2PO4 and correlated with the isotope effect on the high-temperature high-pressure phase relations of KH2PO4. 相似文献
19.
Subhadeep Kal Emil Stoyanov Thomas L. Groy Ulrich Häussermann 《Journal of solid state chemistry》2008,181(11):3016-3023
High-pressure forms of intermetallic compounds with the composition CaZn2, SrZn2, SrAl2, and BaAl2 were synthesized from CeCu2-type precursors (CaZn2, SrZn2, SrAl2) and Ba21Al40 by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl2 and BaAl2), X-ray single-crystal diffraction (CaZn2), and electron microscopy (SrZn2). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu2 (C15) structure, the dizincides adopt the hexagonal MgZn2 (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. 相似文献
20.
Up to ~1 mol % maximum solid solubility of KNO2 or NaNO3, the two solid—solid transition temperatures in NaNO2-base alloys decrease ~11±4 deg per mol % solute, except that the upper transition temperature is hardly altered by alloying with KNO2. From the data on alloys with KNO2, the ratio of the entropy of the upper transition to the lower transition in NaNO2 is estimated as 0.35±0.07. 相似文献