  The geometrically frustrated antiferromagnetic Swedenborgite
DyBaCo$_{4}$O$_{7}$ is investigated by a combination of xray diffraction,
magnetization and dielectric measurements. Systematic doping in the series
Dy$_{1-x}$Ca$_{x}$BaCo$_{4}$O$_{7}$ causes a lifting of the geometrical
frustration resulting in a structural transition from a Trigonal P31c to an
orthorhombic Pbn2$_{1 }$ symmetry at $x=0.4$. This structural transition can
also be accessed as a function of temperature, and all our orthorhombic
specimens exhibit this transition at elevated temperatures. In line with
previous reports, the temperature at which this structural transition occurs
scales linearly with the mean ionic radii of the $A$ site ion. However,
CaBaCo$_{4}$O$_{7}$ which has an equal number of Co${^{2+}}$ and Co${^{3+}}$
ions clearly violates this quasilinear relationship, indicating that charge
ordering could also play a critical role in stabilizing the orthorhombic
distortion in this system. Using thermoremanent magnetization measurements to
circumvent the problem of the large paramagnetic background arising from
Dy${^{3+}}$ ions, we chart out the phase diagram of the
Dy$_{1-x}$Ca$_{x}$BaCo$_{4}$O$_{7}$ series.
