Birefringence of β-LiNH4SO4 crystals with Mn2+ impurity under uniaxial pressures

Single crystals of LiNH4SO4:Mn2+ (5 wt %) were synthesized through the slow evaporation method. The effect of applying uniaxial mechanical pressure along the main physical directions of the crystal on the dispersion and temperature changes of their birefringence is studied. It was discovered that the nature of the behaviour of Delta n(i)(lambda) and Delta n(i)(T) remain unchanged under uniaxial loading, but only the values of d Delta n(i)/d lambda and d Delta n(i)/dT change. Additionally, the introduction of a manganese admixture does not significantly change the baric sensitivity of Delta n(t)(lambda, T) of the beta-LiNH4SO4 crystal. Under uniaxial pressures along the Y direction, the optical isotropic point of the impurity crystal shifts into the long-wavelength part, and along the X direction - into the short-wavelength part of the spectrum. The study also revealed the baric shift of the ferroelectric-paraelectric phase transition point on the temperature scale, the nature of which depends on the direction of uniaxial pressure.