The crystal structures, pyroelectric properties, and thermal stability of [111]-oriented 0.5 mol% Mn-doped 0.36Pb(In1/2Nb1/2)O-3-0.36Pb(Mg1/3Nb2/3)O-3-0.28PbTiO(3) (Mn-0.36PIN-0.36PMN-0.28PT) ternary single crystal were investigated. The temperature dependence of the Raman spectra and dielectric properties revealed that the crystal exhibited a rhombohedral (R) structure at room temperature, and ferroelectric R -> tetragonal (T) and ferroelectric T to paraelectric cubic (C) phase transitions at 130 and 175 degrees C respectively. The single crystal had a high remnant polarization of P-r = 38 mu C cm(-2) and coercive field of E-C = 12 kV cm(-1) at room temperature and a frequency of f = 100 Hz. The values of P-r and E-C decreased with increasing temperature, exhibiting anomalies near their phase-transition temperatures, which coincided with changes in the Raman spectra and dielectric properties. Furthermore, at 25 degrees C and f = 100 Hz, the single crystal had high pyroelectric coefficients of p = 8.7 x 10(-4) C m(-2) K-1, figures of merit for the current responsivity of F-i = 3.5 x 10(-10) m V-1, the voltage responsivity of F-v = 0.08 m(2) C-1, and the detectivity of F-d = 30.1 x 10(-5) Pa-1/2. These values were weakly dependent on temperature below 120 degrees C. In addition, the room-temperature pyroelectric coefficients of the ternary single crystal maintain over 83% of the original value at thermal annealing temperatures below 120 degrees C. These outstanding pyroelectric properties, together with high thermal stability, indicate that [111]-oriented rhombohedral Mn-0.36PIN-0.36PMN-0.28PT ternary single crystal is a new potential candidate for infrared detection applications.