Polymorphic structures and properties of lead chromium phosphate Pb3Cr2(PO4)4

Abstract

Single crystals of lead chromium phosphate Pb 3 Cr 2 (PO 4 ) 4 were grown by a flux technique and characterized by X-ray powder and single crystal diffraction, differential thermal analysis, polarized light microscopy and magnetic measurements. Two polymorphic structures have been identified: a monoclinic Pb 3 Cr 2 (PO 4 ) 4 of space group P2 1 /c ( 14) and a tetragonal Pb 3 Cr 2 (PO 4 ) 4 of space group P4 1 2 1 2 (94), and their phase correlation is described. Both structures consist of a three-dimensional framework which is composed of PO 4 tetrahedra and CrO 6 octahedra connected via vertices. Lead ions are situated at the cavities of the framework, but the positions of lead ions in the monoclinic Pb 3 Cr 2 (PO 4 ) 4 are different from those in the tetragonal Pb 3 Cr 2 (PO 4 ) 4 . The Pb 3 Cr 2 (PO 4 ) 4 crystals are found to exhibit interesting physical properties. The ferroelastic domain structures reveal characteristic patterns of the tetragonal and the monoclinic symmetry of the crystals. The birefringence of the tetragonal crystals decreases with increasing temperature. The monoclinic crystal is found to undergo a series of magnetic phase transitions upon cooling, from a paramagnetic phase (from room temperature down), to an antiferromagnetic phase below T N ¼ 6 K, and then to a weakly ferromagnetic phase below the Curie temperature T C ¼ 4 K, with a magnetic hysteresis loop displayed at 2 K.

Exploring the Colour of 3d Transition‐Metal Ions in Trigonal Bipy­ramidal Coordination: Identification of Purple‐Blue (CoO5) and Beige‐Red (NiO5) Chromophores in LiMgBO3Host

“…We found that the green colour is due to the presence of CrBO 3 . [33] Similarly, Mn III substitution also formed multiple phases consisting of LiMgBO 3 and Li 2 MnO 3 . The red colour of the product is attributed to the presence of Li 2 MnO 3 ; optical absorption spectra ( Figure S6) show features characteristic of Li 2 MnO 3 .…”

Crystal structure of rubidium chromium diphosphate, RbCrP2O7

“…In recent years, inorganic metal phosphates have been part of intensive research activities both in high-temperature solid state and aqueous solution conditions, and their number has grown steadily [1][2][3]. Thec rystal chemistry of these compounds with anionic partial structures mainly built from PO 4 …”