Critical x-ray scattering studies of Jahn-Teller phase transitions in TbV1−xAsxO4

The critical behavior associated with the cooperative Jahn-Teller phase transitions in TbV1−xAsxO4 (where x=0,0.17,1) single crystals have been studied by using high-resolution x-ray scattering. These materials undergo continuous tetragonal→orthorhombic structural phase transitions that are driven by the Jahn-Teller physics at TC=33.26(2), 30.32(2), and 27.30(2) K for x=0, 0.17, and 1, respectively. The orthorhombic strain was measured close to the phase transition and was shown to display mean field behavior in all three samples. Pronounced fluctuation effects are manifest in the longitudinal width of the Bragg scattering, which diverges as a power law, with an exponent given by x=0.45±0.04, on approaching the transition from either above or below. All samples exhibited twinning; however, the disordered x=0.17 sample showed a broad distribution of twins that were stable to relatively low temperatures, well below TC. This indicates that while the orthorhombic strain continues to develop in a conventional mean field manner in the presence of disorder, twin domains are easily pinned by quenched impurities and their associated random strains.