Owing to the effect of atomic vibrations, a high-temperature phase usually features a relatively smaller density when compared with a low-temperature phase. In this work, a new SrCdB₂O₅ phase has been discovered. According to the crystallization temperature from low to high, the new SrCdB₂O₅ phase can be regarded as the high-temperature β-SrCdB₂O₅ phase. The density of β-SrCdB₂O₅ is obviously larger than that of α-SrCdB₂O₅, meanwhile β-SrCdB₂O₅ is energetically favored. This unusual density evolution phenomenon has been investigated. In addition, the Pb²⁺-doped compounds, Pb_xSr_1−xCdB₂O₅ (x = 0.125, 0.25, 0.375, 0.5), have also been investigated by powder refinement.