Pockels coefficient measurements for BTO, with r 33 in dark green, r 42 in light green and model fits to the data in solid lines. The r 42 data are fit to a Debye model with 0 = 565 MHz, = 0.06, S R = 75 pm V –1 and r = 60 pm V –1. The 1/2( r 13 + 2 r 42 ) value is fit using equation ( 5 ), where is calculated from the Debye model of equation ( 2 ) using the same coefficients as the measured permittivity (Table 1 ). The data points are the result of fitting the measured r eff data from n = 15–20 devices to equation ( 4 ), as described in Supplementary Information . The error bars represent two standard errors of the fit. Note that typically 2 r 42 >> r 13 so that r 13 + 2 r 42 2 r 42. We, therefore, plot this parameter as 1/2( r 13 + 2 r 42 ) r 42.
