Low temperature structural phase transition in the Ba2CaMoO6 perovskite

Abstract

Ba2CaMoO6 was synthesized by solid state method. The crystal structure adopts cubic Fm-3m space group at room temperature with lattice parameters of 8.378231(5) Å. Upon cooling, Ba2CaMoO6 was determined to have a structural phase transition to tetragonal I4/m (a=5.905763(6) Å and c=8.38817(1) Å) around 200 K. The phase transition was probed structurally by synchrotron and neutron diffraction and thermodynamically by specific heat and differential scanning calorimetry measurement. This structural phase transition will deepens our understanding of the perovskite family especially the formation of perovskites that break corner sharing networks.

Hexagonal Perovskites as Quantum Materials

“…In classical double perovskites, there are two different "M type" ions in an ordered array or a partially ordered array within the MO3 framework. Double perovskites can be written in the form A2MM'O6, where M and M' can be different ions such as in Sr2FeWO6, a material that has a particularly high magnetoresistance 51 or even the same M metal with different oxidation states, such as is seen in BaBiO3 (Ba2Bi 3+ Bi 5+ O6 formally) [52][53][54][55][56][57] , the basis for superconductivity in several perovskite oxides 58,59 . Disordered and partially ordered M-M' double perovskites are known.…”

Characterization and Rietveld refinements of new dense ceramics Ba3−xSrxTb3−xCexO9 (x = 1 and 1.5) perovskites

“…For X-ray powder diffraction (XRPD) measurements, two factors are considered: (1) in general cases, the high-angle upper-limit 2 θ m is taken to be 120° or larger, which is apt to yield satisfactory refined results in the crystal structure refinement (Chen et al ., 1995) and (2) the possible ordering of Ba 2+ /Sr 2+ at the A-sites or Ce/Tb at the B-sites in the lattice will result in extra peaks, forming a so-called superstructure. The superstructure peaks with higher intensity are easier to be observed in the lower 2 θ range of 10–20°, such as for A-site-ordered perovskites (Li 1/2 Nd 1/2 )TiO 3 (Takahashi et al ., 1991) and (La 1/2 Na 1/2 )TiO 3 (Ioshiyuki et al ., 1992), as well as B-site-ordered perovskites Pb 2 CaTeO 6 (Artner and Weil, 2019), Ba 2 CaMoO 6 (Nguyen et al ., 2019), and Ba 2− x La x FeMoO 6 (Hussain et al ., 2019). For these two factors, the 2 θ ranges in XRPD spectra of BSTC1 and BSTC3/2 are expanded from 5° to 120° and no diffraction peaks between 5° and 20° were observed.…”