Transparent, ferroelectric polymer composites containing nano-particles with a particle size of 1-100 nm, selected from a wide range of mixed metal compounds, e.g. barium lithium niobate, bismuth ferrate, calcium zirconate, lead tantalate, potassium iodate (74 compounds and compound types listed). Transparent, ferroelectric polymer composites (I) containing nano-particles (II) with an average particle size of 1-100 nm, selected from a wide range of mixed metal compounds, e.g. AgNbO3, BaMgF4, Ba2LiNb5O15, BaXF4, BiFeO3, Ca2Nb2O7, CdHfO3, CsCoPO4, ErMnO3, HoMnO3, KIO3, KTaO3, LiTaO3, LuMnO3, NaCdPO4, Nd2Ti2O7, NH4IO3, Pb5Cr3F19, Pr2Ti2O7, RbMnBr3, RMnO3, SbNbO4, ScTaO4, SrAlF5, SrZrO3, TmMnO3, YMnO3 and YbMnO3, in which X : Mn, Fe, Co, Ni, Cu or Zn; R : Sc, Y, In, Ho, Er, Tm, Yb or Lu (74 compounds and compound types listed). Independent claims are included for (1) dispersions (III) containing an organic solvent and (II) (2) a method for the production of (I) by making a transparent dispersion (III) as above, mixing this with a polymer or polymer mixture and then evaporating the solvent, or by mixing (II) with a polymer precursor or solution thereof and then polymerising the mixture by known methods .