Phase transitions in K_1−xRb_xSc(MoO₄)₂ solid solutions

Abstract

K_{1− x} Rb _x Sc(MoO₄)₂ single crystals doped with Cr³⁺ were studied by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy and optical microscopy. It has been found that the EPR spectra in solid solutions for x ≤ 0.2 are inhomogeneously broadened due to the random occupation of the next nearest-neighbour cation sites K⁺ and Rb⁺. The spin-Hamiltonian parameters describing the room-temperature EPR spectra of Cr³⁺ in K_{1− x} Rb _x Sc(MoO₄)₂ are calculated. The behaviour of the EPR spectra versus temperature reveals the existence of structural phase transitions in these crystals. The results show that a substitution of K⁺ by Rb⁺ suppresses the transition temperatures. The optical investigations carried out under the polarizing microscope have shown a ferroelastic nature of these transformations.

Keywords:

• phase transition
• linewidth
• ferroelastics
• light microscopy
• electron paramagnetic resonance
• trigonal double molybdates