Sol-gel synthesis of CaBPO5: phase composition and thermal properties
DOI:
https://doi.org/10.15328/cb2026_174Keywords:
CaBPO5, calcium borophosphate, citrate-assisted sol–gel synthesis, phase formation, powder X-ray diffraction, thermal analysisAbstract
A citrate-assisted sol–gel route was investigated for the preparation of crystalline calcium borophosphate (CaBPO5). To the best of our knowledge, this is the first report of crystalline CaBPO5 obtained by this route. The phase compositions of products prepared with different H3BO3 excesses and precursor-concentration procedures were compared. Concentration under heating produced multiphase products containing CaBPO5 and calcium phosphate secondary phases; increasing the H3BO3 content did not eliminate these impurities. Under optimized conditions, involving 20 mol.% excess H3BO3, a reduced precursor-solution volume, and gel formation at room temperature, crystalline CaBPO5 without secondary phases detectable by powder X-ray diffraction was obtained after thermal treatment. Rietveld refinement confirmed the formation of trigonal stillwellite-type CaBPO5 in the P3121 space group, with unit-cell parameters close to reported values. The Crystallographic Information File (CIF) for the synthesized CaBPO5 sample is available in the Cambridge Structural Database under the registration number CSD 2596463. Differential thermal analysis revealed a high-temperature endothermic event with an onset temperature of 1037.1°C, assigned to the onset of incongruent melting. The study demonstrates the feasibility of citrate-assisted sol–gel synthesis of crystalline CaBPO5 and identifies a combination of precursor-preparation conditions yielding a product without PXRD-detectable secondary crystalline phases.
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