  A calculation of the expected signal due to Primakoff coherent conversion of
solar axions into photons via Bragg scattering in several crystal detectors is
presented. The results are confronted with the experimental sensitivities of
present and future experiments concluding that the sensitivity of crystal
detectors does not challenge the globular cluster limit on the axion-photon
coupling g_a. In particular, in the axion mass window m_a ~> 0.03 eV explored
with this technique (not accessible at present by other methods) g_a might be
constrained down to 10^-9 GeV^-1 (the recent helioseismological bound) provided
that significant improvements in the parameters and performances of these
detectors be achieved and large statistics accumulated. This bound should be
considered as a minimal goal for the sensitivity of future crystal experiments.
Consequently, finding a positive signal at this level of sensitivity would
necessarily imply revisiting other more stringent astrophysical limits derived
for the same range of m_a values.
