Oriented films of polyvinylidene fluoride [(CH2CF2)n], a polar polymer possessing symmetry mm2, can be made significantly pyroelectric and optically nonlinear by poling in an electric field. A pyroelectric coefficient (dP/dT = 2.4 ± 0.7 nC/cm2°C) comparable to that of single-crystal LiNbO3 is observed. The nonlinear optical coefficients d33, d32, and d31 of polyvinylidene fluoride (PVF2) are measured relative to d11 of crystalline quartz [d33 (PVF2)≃2d31 (PVF2) ≃d11(SiO2); d32(PVF2)≃0]. The poled films have specific advantages for pyroelectric detection of electromagnetic radiation and for optical parametric devices.

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The symmetry properties of potassium iodate have been investigated in order to determine whether it might be a useful nonlinear optical material. In order to resolve the confusion over the point symmetry of this material, several experimental techniques have been used. These are single‐crystal X‐ray diffraction (room temperature), optical examination using conoscopic methods, second harmonic generation powder test, and pyroelectric measurements (the latter three techniques covering various temperature ranges). Correlating these observations with previously reported properties of KIO3 yields the result that below 212 °C, KIO3 is monoclinic Cm with a0 = 8.86 (5), b0 = 12.54 (6), c0 = 7.70 (5) Å and β = 125°05′±20′. The material is negative biaxial with 2V = 20°30′±30′ and pyroelectric with dPs/dT = 5.8 × 10−9 Coul. cm−2°C−1 (at room temperature). Above 212 °C this material is rhombohedral R3m with a0≃7.70 and α≃ 109°28′. The nature of the twinning below 212 °C and a method of detwinning are discussed. Type one phase matching angles were calculated.

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We report our measurements on KIO2F2 and compare these results with the parent MIO3 compounds where M denotes H, Li, etc. Our results show that the nine observed nonlinear coefficients (d's) in these four different crystal systems, composed of IO3− and IO2F2− ions, are geometrically related to only one microscopic bond polarizability (β), the ∥ and ⊥ components of which are (3.6±0.4)×10−30 esu and (1.0±0.1)×10−30 esu, respectively. We further report that the nonlinear polarizability of the iodine lone pair is equivalent to that of an iodine-oxygen bond ∼1.85 Å. Microscopic theories relate the observed bulk nonlinear coefficients (d's) to the individual bond polarizabilities (β's) via [d = Σ(G∥β∥+G⊥β⊥)], where (β∥,β⊥) represent the ∥ and ⊥ components of the bond polarizabilities, respectively, and (G∥,G⊥) are the appropriate geometrical factors, viz., unit cell volumes and direction cosines of the bonds. Current theories maintain that β⊥ can be neglected since β∥≫β⊥. We find that while β⊥ is indeed smaller than β∥, it is not negligible, i.e., β∥∼ 3.6β⊥ for iodine-oxygen bonds. We further find that in certain cases G⊥∼ 10G∥. These two observations, which show that G∥β∥ ∼ G⊥β⊥, being previous calculations of β's and d's based on setting β⊥=0 into serious question.