Losses in piezoelectrics are approached by considering a description of direct stress-charge displacement hysteresis. Shortcomings of the usual loss models (viscous and Rayleigh, taken separately) are briefly demonstrated. Then, a mixed model for piezoelectric losses superimposing viscous and Rayleigh types of descriptions is proposed and validated for a modified lead titanate and lead zirconate titanate (PZT). It is shown for PZT that viscous and Rayleigh-like loss contributions can be effectively separated by fitting the piezoelectric hysteresis loop with an expression combining the two lossy responses. The possibility to obtain all the necessary parameters that describe piezoelectric stress nonlinearity from one single piezoelectric loop is also demonstrated in the case of PZT. The origins of the mixed loss behavior are interpreted as arising from domain wall motion in terms of internal friction mechanisms and of pinning energy ranges. (C) 2001 American Institute of Physics.