PHYSICAL REVIEW B, cilt.83, 2011 (SCI İndekslerine Giren Dergi)
We report a high resolution neutron diffraction investigation of the coupling of structural and magnetic transitions in Ba1-xKxFe2As2. The tetragonal-orthorhombic and antiferromagnetic transitions are suppressed with potassium doping, falling to zero at x less than or similar to 0.24. However, unlike Ba(Fe1-xCox)(2)As-2, the two transitions are first order and coincident over the entire phase diagram, with a biquadratic coupling of the two order parameters. The phase diagram is refined showing that the onset of superconductivity is at x = 0.133 with all three phases coexisting until x <= 0.24.