Preparation and properties of Dion–Jacobson-type perovskite CsA2Nb3O10 (A = Ca, Sr, Ba) crystals and ceramics by the molten salt method

Dion–Jacobson-type (DJ-type) perovskite CsA 2 Nb 3 O 10 (A = Ca, Sr, Ba) is a compound that can simultaneously accommodate Cs + and A 2+ ions and thus considered as a potential immobilization matrix for radionuclides 137 Cs and 90 Sr. In this work, using A 2+ to simulate bivalent alkaline earth metals, CsA 2 Nb 3 O 10 single crystals were synthesized by the molten salt method. CsA 2 Nb 3 O 10 has good thermal stability up to 900°C. At the same time, CsA 2 Nb 3 O 10 has strong radiation resistance, with most crystals maintain their initial morphology with slight color change. Cations with smaller radii, for example, Na + , K + , and Rb + , do not replace Cs + in the interlayer of CsA 2 Nb 3 O 10 and A 2+ in the NbO 6 polyhedron. CsA 2 Nb 3 O 10 demonstrates a wide range of pH durability, where its frame structure remains stable in the pH range from 2 to 12 and will not be decomposed, while Cs + in CsA 2 Nb 3 O 10 loses more into the solution at the pH range from 2 to 4 and from 10 to 12, and the loss of Sr 2+ and Ba 2+ is much lower than that of Ca 2+ due to slight differences in the framework structure. Further sintering of CsCa 2 Nb 3 O 10 and CsSr 2 Nb 3 O 10 result in high density ceramic with a relative density of 94%–97%, along with improved chemical stability. According to the investigation of the surface morphology and elemental chemical state, it can be confirmed that Cs, A, and Nb elements are uniformly distributed on the surface of ceramics. The normalized leaching rates of Cs, Ca, and Sr in the CsCa 2 Nb 3 O 10 and CsSr 2 Nb 3 O 10 ceramic waste forms are about 1, 1, and 10 −4 to 10 −3 g·m −2 ·d −1 after 28 days, respectively.