A meta-stable ferroelectric structure including one of the following oxides: an isovalent combination of the formula MxM′1-xO2-δ, wherein M, M′={Zr, Hf, Pb, W, Mo, Nb, Te, Ti}, 0≤x≤1, 0≤δ≤0.5 excluding {HfxZr1-xO2 all x in Pca21 phase}; an aliovalent combination of the formula MIxMII1-xO2-δ, wherein MI, MII={Bi, Y, Ta, In, Mo, Nb, Sc, Tl, Pd, Sb, W, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Pd, Ni, Ru, Hg}, 0≤x≤1, 0≤δ≤0.5, excluding certain aliovalent combinations; or an isovalent-aliovalent combination of the formula MxMIyMII1-x-yO2-δ, wherein M, MI, and MII are as set forth above, 0≤x≤1, 0≤y≤1, 0≤δ≤0.5; wherein the ferroelectric structure is in a Pca21 or Pmn21
space group or a subgroup thereof.