Time-resolved electric-field neutron-diffraction experiments in the microsecond range

John Daniels and Trevor Finlayson (Monash U.), Andrew Studer(ANSTO) and Mark Hagen(ORNL)

We have developed a new capability (shown above) to observe diffraction intensities in real time during the application of electric-field pulses, using a stroboscopic technique. We have applied continuous high-voltage pulses to samples in the beam, on the HIFAR Strain Scanner: during these pulses, neutrons detected at the position-sensitive detector are not only binned in 2θ, but also as a function of time within one period of the electrical pulse.The apparatus is capable of switching voltages of up to 10kV at frequencies up to 10kHz.

Our timing resolution is approximately 25μs, which allows for the observation of structural relaxations occurring over a times greater than 25μs.

Our initial experiments have involved the switching of single crystals of triglycine sulphate from the paraelectric disordered state to a ferroelectric ordered state. The most interesting results are observed in the behaviour of the (060) Bragg peak as a function of time, during the application of a 500Hz square wave with a field strength of 4.8kV/cm.Figure 1 shows the behaviour of the (060) peak over the duration of the 2ms electric field pulse.

Figure 2 shows a more detailed view of the relaxation in the (060) Bragg peak after the removal of a 4.8kV/cm field at time = 0. Here we see how the intensity spikes sharply before relaxing back to its field off value over approximately 150µs.

Figure 1. (060) Bragg peak intensity of TGS during the application of a 500Hz square wave, field on from 0-1ms, field off 1-2ms. Data were separated into 200 time frames within the 2ms cycle.

Figure 2. Relaxation of (060) Bragg peak intensity after the removal of a 4.8kV/cm field. The upper and lower dashed lines represent the field on and field off intensities during the application of the 500Hz square wave respectively.