title: Temperature dependent structural, vibrational and magnetic properties of K3Gd5(PO4)6.
abstract: Herein we report the evolution of the crystal structure of K3Gd5(PO4)6in the temperature range from 20 K to 1073 K, as observed from variable temperature X-ray diffraction and Raman spectroscopic studies. K3Gd5(PO4)6has an open tunnel containing a three dimensional structure built by [Gd5(PO4)6]3-ions which in turn are formed of PO4tetrahedra and GdOn(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: αa= 10.6 × 10-6K-1, αb= 5.5 × 10-6K-1and αc= 16.4 × 10-6K-1. The evolution of distortion indices of the various coordination polyhedra with temperature indicates a gradual decrease with increasing temperature, while those of Gd2O9and K2O8polyhedra show opposite trends. The overall anisotropy of the lattice thermal expansion is found to be controlled largely by the effect of temperature on GdOnpolyhedra 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 K3Gd5(PO4)6compared 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 Gd3+ion and the Weiss constant are 7.91 μBand 0.38 K, respectively.
authors.affiliation: Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India. sachary@barc.gov.in acharysn@rediffmail.com and Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India.
authors.forename: Samatha
authors.initials: S
authors.lastname: Bevara
authors.affiliation: Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India. sachary@barc.gov.in acharysn@rediffmail.com and Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India.
authors.forename: S Nagabhusan
authors.identifier: http://orcid.org/0000-0002-2103-1063
authors.initials: SN
authors.lastname: Achary
authors.affiliation: Condensed Matter Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India.
authors.forename: Karuna Kara
authors.initials: KK
authors.lastname: Mishra
authors.affiliation: Condensed Matter Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India.
authors.forename: T R
authors.initials: TR
authors.lastname: Ravindran
authors.affiliation: Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India and Indus Synchrotron Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Sinha
authors.affiliation: Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: P U
authors.initials: PU
authors.lastname: Sastry
authors.affiliation: Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India. sachary@barc.gov.in acharysn@rediffmail.com and Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India.
authors.forename: Avesh Kumar
authors.initials: AK
authors.lastname: Tyagi