Growth and characterization of perovskite LaGaO3 crystals doped with Sr and Mn

Single crystals of LaGaO3 doped with Sr and Mn (LSGMn) were grown by the Czochralski method from the melt with compositions: La1−xSrxGa1−yMnyO3, x = y = 0.02; 0.05 and x = 0.05, y = 0.06. Single crystals with 20 mm diameter with convex crystal–melt interface were grown on LaGaO3 oriented seed with pulling rate of 2 mm/h. Single crystals were dark and have strong tendency to spiral growth. This tendency was decreased with increasing the Mn content in comparison with Sr. Effective segregation coefficients for Sr and Mn in LaGaO3 are lower than 1. Room-temperature structural measurements by X-ray powder diffraction showed perovskite structure with Pbnm space group for all measured samples. Orthorhombic b and c lattice parameters decrease, whereas a slightly increases with decreasing orthorhombic unit cell volume that is related to increased amount of Mn and Sr in the melt. Thermal analysis and Raman investigations showed that the temperature of the first order phase transitions temperature form orthorhombic to rhombohedral structure observed in pure LaGaO3 at about 150 °C decreases to about 49 °C at the bottom part of crystal with x = y = 0.05 composition.

Research highlights▶ b and c lattice parameters of La1−xSrxGa1−yMnyO3 crystals decrease, whereas a slightly increases resulting in decreasing orthorhombic unit cell volume that is related to increased amount of Mn and Sr in the melt ▶ Observed decrease of unit cell volume vs. Sr and Mn content in La1−xSrxGa1−yMnyO3 crystals is most probably a superposition of two mechanisms—enlargement with Sr content (r(Sr2+) 1.44 Å > r(La3+) 1.36 Å) and contraction with Mn content (r(Mn4+) 0.53 Å < r(Ga3+) 0.62 Å) ▶ The O/R phase transition temperature decreases from 148.5 °C to 48.8 °C with decreasing size of the orthorhombic unit cell volume that is related to increased amount of Mn and Sr in the melt.