Аннотация:Double borate Na3ErB2O6 was synthesized by the solid-state reaction.The crystal structure of Na3ErB2O6 was refined by the Rietveld method: P21/c, a = 6.49775(14) Å, b = 8.50424(17) Å, c = 12.0067(3) Å,β = 118.4797(9)°, Z = 4. The crystal structure of Na3ErB2O6 consistsof –[ErO6]∞-chains along the "b" axis, which are linked by BO3 triangles in a three-dimensional framework. Sodium atoms occupy emptypositions inside the channels. The thermal behavior of Na3ErB2O6was studied in detail in the range of 25–1150 °C range by DSC and TGmethods. Na3ErB2O6 congruently melts at 1116 °C. Based on the results of DSC measurements, three reversible phase transitions werefound for Na3ErB2O6.