Complex sentence: The crystallography and thermodynamics of the R-phase are now well understood, but it still creates many complexities in device engineering, leading to the well-worn phrase, "It must be the R-phase" whenever a device fails to perform as expected.
Split into simpler sentences: The crystallography and thermodynamics of the R-phase are now well understood, but it still creates many complexities in device engineering. According to awell-worn phrase, "It must be the R-phase" whenever a device fails to perform as expected.