Room temperature multiferroism in CaTcO$_3$ by interface engineering

The structural instabilities of ATcO$_3$(A= Ca, Sr, Ba) are investigated by first-principles calculations. In addiction to the large octahedral rotation instability, a weak ferroelectric tendency is identified in CaTcO$_3$. We show that the ferroelectricity in CaTcO$_3$ can be recovered by interface engineering based on CaTcO$_3$/BaTcO$_3$ superlattices, where the octahedral rotation is largely suppressed. The N{\'e}el temperature is found to be $\sim$ 816 K, indicating that CaTcO$_3$ can be engineered into a new room temperature multiferroic material.