Ultralow Detection Limit and Anisotropic X‐Ray Detection Behaviors Based on A Novel Oxide KCsMoP₂O₉ Single Crystal

X‐ray detection has drawn great attention in industrial examination, medical imaging, scientific research, and beyond. Herein, the anisotropic X‐ray detection performances are investigated based on a novel oxide crystal KCsMoP 2 O 9 (KCMP). The large dielectric screening effect and 1D infinite chain structure consisting of MoO 6 octahedron and two PO 4 tetrahedrons are conducive to efficient carrier transport along the X‐direction, leading to a higher µτ (4.77 × 10 −3 cm 2 V −1 ) of X direction than that of Z direction (1.05 × 10 −4 cm 2 V −1 ). Additionally, the KCMP‐based X‐ray detector along the X direction shows weaker ion migration than that of the Z direction due to the large migration barrier of O 2− (8.0 eV) and high ion active energy (784.9 meV) along the X direction. Owing to the high resistivity (2.29 × 10 13 Ω cm), high µτ, high ion activation energy, suppressed ion migration, and ultralow dark current, the X‐ray detection performance of the KCMP detector along the X direction is superior to that of the Z direction. Specifically, the high sensitivity (131.2 µC Gy −1 cm −2 ) and ultralow detection limit (8.9 nGys −1 ) are achieved in the KCMP detector along the X direction. This work clarifies anisotropic engineering to enhance the X‐ray detection performance of oxide crystals and proposes a novel X‐ray detection crystal with an ultralow detection limit.