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Structure-preserving doubling algorithms (SDAs) are efficient algorithms for solving Riccati-type matrix equations. However, breakdowns may occur in SDAs. To remedy this drawback, in this paper, we first introduce -symplectic forms (-SFs), consisting of symplectic matrix pairs with a Hermitian parametric matrix . Based on -SFs, we develop modified SDAs (MSDAs) for solving the associated Riccati-type equations. MSDAs generate sequences of symplectic matrix pairs in -SFs and prevent breakdowns by employing a reasonably selected Hermitian matrix . In practical implementations, we show that the Hermitian matrix in MSDAs can be chosen as a real diagonal matrix that can reduce the computational complexity. The numerical results demonstrate a significant improvement in the accuracy of the solutions by MSDAs.