  We report a systematical structural, transport and magnetic study of Ca or Ba
doped Sr2IrO4single crystals. Isoelectronically substituting Ca2+ (up to 15%)
or Ba2+ (up to 4%) ion for the Sr2+ ion provides no additional charge carriers
but effectively changes the lattice parameters in Sr2IrO4. In particular, 15%
Ca doping considerably reduces the c-axis and the unit cell by nearly 0.45% and
1.00 %, respectively. These significant, anisotropic compressions in the
lattice parameters conspicuously cause no change in the N\'eel temperature
which remains at 240 K, but drastically reduces the electrical resistivity by
up to five orders of magnitude or even precipitates a sharp insulator-to-metal
transition at lower temperatures, i.e. the vanishing insulating state
accompanies an unchanged N\'eel temperature in (Sr1-xAx)2IrO4. This observation
brings to light an intriguing difference between chemical pressure and applied
pressure, the latter of which does suppress the long-range magnetic order in
Sr2IrO4. This difference reveals the importance of the Ir1-O2-Ir1 bond angle
and homogenous volume compression in determining the magnetic ground state. All
results, along with a comparison drawn with results of Tb and La doped Sr2IrO4,
underscore that the magnetic transition plays a nonessential role in the
formation of the charge gap in the spin-orbit-tuned iridate.
