The boundary-value problem of the dynamic Bragg diffraction of optic radiation in the Laue geometry in a 1D passive PT-symmetric photonic crystal (PhC) is solved using the analytic spectral method. It is shown that the Borrmann effect, or anomalously high transparency of the crystal with the fulfillment of the Bragg condition in a passive PT-symmetric PhC, has a number of peculiarities that can be explained by the existence of an exceptional point of spontaneous breaking of the PT-symmetric component of radiation modes. For example, in the Borrmann effect, the diffracted wave amplitude increases due to intensification of absorption in the medium. This is observed near the exceptional point above the threshold value of the absorption parameter for a positive Bragg angle of radiation incidence on the crystal. Asymmetry of the Borrmann effect in a passive PT-symmetric PhC is also observed: the amplitude of the diffracted wave changes upon the sign reversal of the Bragg angle (increases in the case of a negative angle of incidence).
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