Temperature dependent structural, vibrational and magnetic properties of K3Gd5(PO4)6. Issue 8 (10th February 2017)

• Record Type: Journal Article
• Authors: Bevara, Samatha; Achary, S. Nagabhusan; Mishra, Karuna Kara; Ravindran, T. R.; Sinha, Anil K.; Sastry, P. U.; Tyagi, Avesh Kumar
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 8(2017)
• Page Start: 6030
• Page End: 6041
• Publication Date: 2017-02-10
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp08086c
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Anisotropic thermal expansion ( α c > α a ≫ α b ) and vibrational properties of K3 Gd5 (PO4 )6 . Abstract : Herein we report the evolution of the crystal structure of K3 Gd5 (PO4 )6 in the temperature range from 20 K to 1073 K, as observed from variable temperature X-ray diffraction and Raman spectroscopic studies. K3 Gd5 (PO4 )6 has an open tunnel containing a three dimensional structure built by [Gd5 (PO4 )6 ] 3− ions which in turn are formed of PO4 tetrahedra and GdO n ( n = 8 and 9) polyhedra. The empty tunnels in the structure are occupied by K + ions and maintain charge neutrality in the lattice. Evolution of unit cell parameters with temperature shows a systematic increase with temperature. The average axial thermal expansion coefficients between 20 K and 1073 K are: α a = 10.6 × 10 −6 K −1, α b = 5.5 × 10 −6 K −1 and α c = 16.4 × 10 −6 K −1 . The evolution of distortion indices of the various coordination polyhedra with temperature indicates a gradual decrease with increasing temperature, while those of Gd2O9 and K2O8 polyhedra show opposite trends. The overall anisotropy of the lattice thermal expansion is found to be controlled largely by the effect of temperature on GdO n polyhedra and their linkages. Temperature dependent Raman spectroscopic studies indicated that the intensities and wavenumbers of most of the Raman modes decrease continuously with increasing temperature. Anharmonic analyses of Raman modes indicated that the lattice, rigid translation and librational modes have larger contributions towards thermal expansion of K3 Gd5 (PO4 )6 compared to high frequency internal modes. The temperature and field dependent magnetic measurements indicated no long range ordering down to 2 K and the observed effective magnetic moment per Gd 3+ ion and the Weiss constant are 7.91 μ B and 0.38 K, respectively.