Expanding gaudefroyite family to Sr2MBi(REEO)3(BO3)4 (M = Ca, Sr, Ba; REE = Y, Eu) borates with large second harmonic generation responses

The synthesis, crystal structure, and characterization of a few new noncentrosymmetric rare-earth borates of gaudefroyite family Sr2MBi(REEO)3(BO3)4 (M = Ca, Sr, Ba; REE = Y, Eu) are represented. Samples of Sr2MBi(YO)3(BO3)4 (M = Ca, Sr, Ba) borates were synthesized by multi-step solid state reactions. The crystal structures of Sr3Bi(YO)3(BO3)4, Sr2CaBi(YO)3(BO3)4 and Sr2BaBi(YO)3(BO3)4 were refined in P63 space group to R1 0.059, 0.058 and 0.018, respectively. Second-harmonic generation measured with Kurtz-Perry powder technique shows an increase in the nonlinear optical activity of materials by almost two times upon partial substitutions of Sr for Ca and Ba in the Sr3Bi(REEO)3(BO3)4 and its decrease if Y atoms are replaced by Eu. Thermal expansion coefficients for Sr2MBi(YO)3(BO3)4 (M = Ca, Sr, Ba) borates and Ca4(MnO)3(BO3)3(CO3) gaudefroyite are calculated for the first time. Thermal expansion of these compounds is almost isotropic due to the arrangement of BO3 units which are located in the ab and ac planes.