C. Parada

Synthesis, thermal decomposition and vibrational spectra of the phases MICr(CrO4)2 (MI = Na, K, Rb)

Abstract An alternative method for the synthesis of polycrystalline samples of the phases MICr(CrO4)2 (MI = Na, K, Rb) is proposed. Crystallographic data of the three isostructural compounds were refined by means of the Rietveld method and their thermal stabilities investigated by TG and DTA methods. The infrared and Raman spectra were interpreted on the basis of a factor group analysis of the internal vibrations of the CrO42− groups.

Ca-Zr-O system: synthesis and characterization of compounds using several routes of preparation

Abstract Sol-gel techniques are extensively studied as convenient routes for preparation of oxides in the form of fine powders and for this reason have gained noticeable consideration with regard to both scientific and application purposes. The authors have used this process in the synthesis of oxides in the system Ca-Zr-O. The preparation of perovskite, CaZrO3, and the Φ phases: Φ1(CaZr4O9), Φ(Ca2Zr7O16) and Φ2(Ca6Zr19O44) were attempted by employing several routes: (a) ceramic met hod; (b) oxalated mixed procedure; and (c) the sol-gel technique, in which the reactants used were zirconium propoxide and calcium propionate. The characterization of compounds has been studied by X-ray diffraction and their crystallization by thermal analysis (thermogravimetry, differential thermogravimetry and differential thermal analysis).

Crystallographic data, magnetic and vibrational properties of the series Ln(OH)CrO4 (Ln≡La,Pr,Nd)

Abstract The synthesis of two new rare-earth hydroxochromates, Pr(OH)CrO4 and Nd(OH)CrO4, is described. Their crystallographic data are reported and compared with those of the isostructural lanthanum compound. The vibrational (IR and Raman) spectra of the three compounds, as well as that of the deuterated analogue, La(OD)CrO4, are described and discussed. The magnetic behaviour, in the temperature range between 4.2 and 300 K, was also investigated.

Synthesis, crystallographic data, magnetic properties and vibrational study of the new series KLn(CrO4)4 (Ln = Eu, Gd, Tb)

Abstract Single crystals of the new series KLn(CrO 4 ) 2 were grown by the hydrothermal method. Lattice dimensions decrease from Eu to Tb due to the lanthanide contraction. Magnetic susceptibility measurements were made in the 4.2–300 K temperature range. A vibrational study (I R and Raman) was made using a correlation between the point group of the “free” ions ( T d ), its site symmetry ( C 1 ) and its factor group ( D 2 ).

Magnetic properties and vibrational study of KLn(CrO4)2 (LnY, DyLu)

Abstract Magnetic susceptibility measurements of the last series of KLn(CrO 4 ) 2 (LnY, DyLu) were made in the temperature range 4.2–300 K. Raman and IR spectra were recorded and studied using factor group analysis. These substances shown intercalation of v 1 between v 3 components in crystalline chromates.

A study of ionic conductivity in double rare-earth chromates

Abstract The ionic conductivity of some double rate-earth chromates MLn(CrO 4 ) 2 (M=Na, K, Rb; Ln=La, Eu, Lu) has been analyzed by means of admittance spectroscopy. Real and imaginary part of the permittivity show the frequency power dependence characteristic of many-body interactions between mobile ions. Ac conductivity parameters are correlated with structural details of the compounds studied.

On rubidium lanthanide double chromates

Abstract Synthesis and crystallographic data are reported for a family of double rubidium-rare earth chromates RbLn(CrO 4 ) 2 , where LnLaLu, Y and Sc. The compounds are closely related to the potassium chromates KLn(CrO 4 ) 2 but with a slightly different distribution of structural types: those of La, Pr and Nd are monoclinic, Sm, Eu, Gd are orthorhombic and those of Tb-Lu are also monoclinic but with another unit cell. RbSc(CrO 4 ) 2 has high and low temperature forms: hexagonal and monoclinic respectively. Lattice parameters of all the above compounds are given. Thermal decomposition takes place over 450 °C leading to the rare earth chromites and Cr 2 O 3 .

Synthesis, thermal decomposition, magnetic properties and vibrational study of the series Ln(OH)CrO4 (Ln=Y,DY-Lu)

Abstract Single crystals of the isostructural series Ln(OH)CrO 4 , Ln=Y,Dy-Lu, were grown by the hydrothermal method. They crystallize in the monoclinic system, P 2 1 / n and Z =8. The lattice parameters decrease when the atomic number of the lanthanide cations increases, owing to the lanthanide contraction. Thermal decomposition in nitrogen flow, magnetic behaviour in the 4.2–300 K temperature range and vibrational spectra (IR and Raman) of these compounds have been investigated.

Crystal growth, reactivity and properties of KLn(CrO4)2 (Ln=La, Pr, Nd, Sm and Eu)

Abstract KEu(CrO 4 ) 2 appears to be the last member of the KLn(CrO 4 ) 2 family if isostructural chromates for which Ln is a light rare earth trivalent cation. They have monoclinic symmetry, P2 1 /c and Z =4. The lattice parameters decrease when the atomic number of the lanthanide cation increases. Thermal decomposition either in nitrogen flow or under vacuum and magnetic properties have been also studied.

Thermal decomposition, vibrational study and magnetic properties of Ln2(CrO4)3·7H2O(Ln=La−Eu)

Abstract The thermal decomposition of Ln2(CrO4)3·7H2O was studied by TG, DTG and DTA. The spectroscopic study was carried out using IR and Raman techniques, in addition, the magnetic properties between 4.2–300 K were investigated for this series.