where 8eee6010953e079aa33" title="Click to view the MathML source">0<α<1, iα denotes the principal value of iα, 8e23d" title="Click to view the MathML source">T>0, 999c60c497aa908" title="Click to view the MathML source">λ∈C∖{0}, e9d9bde7a444d1e4e8d4d8a" title="Click to view the MathML source">p>1, u(t,x) is a complex-valued function, and e8077617b25440d2744a224cc1c946"> denotes Caputo fractional derivative of order a9ba690ccbd23a33b4dd0e3d01f40" title="Click to view the MathML source">α. We prove that the problem admits no global weak solution with suitable initial data when 8ed5a21ae8e733bba976" title="Click to view the MathML source">1<p<1+2∕N by using the test function method, and also give some conditions which imply the problem has no global weak solution for every e9d9bde7a444d1e4e8d4d8a" title="Click to view the MathML source">p>1.