Аннотация:Currently, borates attract the attention of researchers, as they are promising nonlinear materials. Potassium rubidium aluminum borate based on potassium aluminum borate (trigonal syngony, space group P321, Z=3) was obtained by solid-phase synthesis. The individuality and purity of the borates were confirmed by X-ray diffraction. Analysis of differential scanning calorimetry and thermogravimetric method for K2(1-x) Rb2x Al2 B2 O7 (x=0.1–0.8) was performed in the temperature range of 25–1075°С. Potassium rubidium borates decompose in the temperature range of 900–1000°C. Differential scanning calorimetry, dielectric loss tangent, and second-harmonic generation data revealed phase transitions for K0.6Rb1.4Al2 B2 O7 . A significant SHG effect was found at room temperature for K0.6Rb1.4Al2 B2 O7 (Q=70). Then the SHG effect increases to Q=85 at a temperature of 645°C and remains constant with a further increase in temperature. The new triple borate Cs1.39Tl0.61Al2 B2 O7 was synthesized by the solid-phase synthesis, and its crystallographic parameters were obtained by the Rietveld method. This borate crystallizes in the monoclinic space group P21/c with the unit cell parameters: Z=2, a=6.6669(3) А˚ , b=7.2991(3) А˚ , c=9.3589(4) А˚ , β=116.6795(18)°, V=406.94(3) А˚ 3 . The structure can be considered to be built up from the nearly planar [Al2 B2 O10] rings, which are composed of two AlO4 tetrahedra and two BO3 triangles, connected, alternately to each other by corner-sharing.