Research On The Optical And Magnetic Properties Of 4d Transition Metal Oxide SrTcO₃

Tuning the band gap of a single-phase perovskite oxide is an effective way to increase the solar cell efficiency. First-principles method based on density functional theory is employed to examine the band gap of 4d transition metal oxide SrTcO3 and its strain effect. It is found that a GGA+U(U =2. 3eV, J =0. 3eV) calculation for SrTcO3 can produce a magnetic moment of 2.10 μB per Tc, in agreement with the experimental result. The corresponding optical band gap is found to be 1.61 eV. Based on the band structure calculations, we find the band gap is of direct band gap character. It is thus suggested to be a good candidate for a solar cell. For application purpose, we study the strain effect on optical band gap of SrTcO3. When the compressive strain is less than 1.58%, the band gap keeps the direct band gap character. And the band gap value does not change much, ranging from 1.533 eV to 1.586 eV, which is close to the optimal band gap given by Shockley-Queisser formula. Hence SrTcO3 is of great potential to fabricate a high-efficiency solar cell. When the compressive strain is larger than 1.58%, the band gap becomes an indirect one, which is unfavorable for absorbing solar energy effectively. Furthermore, DFT and Heisenberg model are combined to calculate the Néel temperature of SrTcO3, and the strain effect on Néel temperature is also examined. It is found that, when the compressive strain is up to 1.41%, the Néel temperature arrives at a maximum value of 1410 K, which is 21.9% higher than the value in the free-standing compound. This particular strain condition can be achieved by growing SrTcO3 on SrTiO3 substrate. Our study shows that devices based on SrTcO3 work well at room temperature or high-temperature circumstances.