Phenomenological theory with nonlocal electrostatics for non-Ising polarization switching and domain walls in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>LiNbO</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:math> and <

We develop the Ginzburg-Landau-Devonshire phenomenological model for trigonal ferroelectrics, which matches experimental values of the poling electric field for both near-stoichiometric and congruent compounds. The model favors a non-Ising type of polarization switching. Therefore, domain walls have nontrivial Néel and/or Bloch polarization components supported by numerical computations. Néel and/or Bloch polarization components are of the order from 1 to 10% of spontaneous polarization in the model. Numerically calculated optimal domain wall profile has bichiral Bloch behavior for near-stoichiometric <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>LiTaO</a:mi> <a:mn>3</a:mn> </a:msub> </a:math> and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>LiNbO</b:mi> <b:mn>3</b:mn> </b:msub> </b:math> and congruent lithium niobate. The domain wall has a mixed Bloch-Néel type without including electrostatic interactions and has a Bloch character when nonlocal electrostatic interactions are accounted for in congruent lithium tantalate.