Fig. 3: Powder diffraction results.
From: Structural origins of dielectric anomalies in the filled tetragonal tungsten bronze Sr2NaNb5O15
Plots of the temperature evolution of (a) the displacive distortion amplitudes for the Ama2 model (five outlying data points removed across two temperatures where refinements adopt false minima; see Supplementary Fig. 16b for full data), and with a critical exponent fit assuming second-order behaviour shown for \({\Gamma }_{3}^{-}\) above 0 °C (Tc = 121.8(13) °C); (b) a and b and (c) c axis cell lengths from VT-PXRD Rietveld refinements using data from Diamond Light Source (Ama2 and Aa models) and Taiwan Photon Source (Cmm2 + k Pawley refinement); (d) symmetry-adapted strains; (e) incommensurate component of the propagation vector, ki, for the observed superstructure, presented with respect to the tetragonal cell; and (f) β angle in the Aa model. Regions corresponding to the T1 and T2 maxima in permittivity are highlighted in blue and red, respectively. Error bars are present and show the 3σ standard uncertainty for (b), (c), and (f); for clarity they are omitted and in the order of 10% for non-zero mode values in (a) and (d) and ~0.015 for (e), while the systematic trends give better estimate of the true precision. For both datasets, high-temperature data were collected first, with temperature increasing, followed by low-temperature data, also with temperature increasing; the discontinuity between low and high-temperature sweeps is due to hysteresis in sample behaviour.
