Stark effect of₁₄N NQR in single crystals of ferroelectric NaNO₂

Abstract

The effects of the external electric field on 14N nuclear quadrupole resonance (NQR) have been investigated in the ferroelectric phase of sodium nitrite (NaNO,) single crystals with either the single domain or the multidomain structure. NQR measurements of two resonance lines of v + and u -were made at 77 K under the external electric field up to 25 kV/cm. The rates of the Stark shift in the crystal of single domain are du+/dE+ = 6.8 f 3.0, dv'ldE-= -9.8 f 2.2, dv-ldE' = 5.0 f 2.0, and dv-/dE-= -2.5 f 2.4 Hz . cm/kV, respectively. Also the rates of the line broadening in the crystal of multidomain can be expressed by d(Av+)/dE+ = 18 f 3 and d(Av+)/dE-= 12 f 3 Hz . cm/kV, respectively. These results are found to be consistent with the sum of two slopes of the v + line with the single domain. The present work provides valuable information on the state of the ferroelectric domains and be applicable to other ferroelectric materials with the 180" domain.

Electric Field Effect on 14N NQR in Ferroelectric Thiourea Single Crystals

“…Since the electric field gradients at the two 14 times those previously reported for NaN0 2 [8,9] and listed in Table 2.…”

“…Experimental evidence [5,8,9] revealed that the shift of NQR frequency is up (down) for £ + (£_) with respect to the spontaneous polarization. When an electric field is applied to a crystal for NQR measurements, a polarization is induced; the electric field applied along the ferroelectric axis increases (reduces) the P s of the crystal for E^P S {EUP S ).…”

“…Since we measured the Stark shift of several lines for the thiourea single crystal, we believe our results are more reliable. 0.0068 [8], [9] * for the v line.…”

“…Likewise, the applied electric field produces observable changes in the electric field gradient (e.f.g.) at the resonant nuclear site [5][6][7][8][9]. When this site has no inversion symmetry of the lattice, the linear effect in the applied electric field may be described phenomenologically by the relation e{Aq) tJ = R klJ E k , (1) where R is a third rank tensor between the change in the field gradient tensor eAq and the applied electric field E [5].…”

“…The Stark effect appears to be remarkably dependent upon the bonding properties such as the ionic or molecular bonding of the crystal. The Stark shifts in thiourea are compared with those previously reported for sodium nitrite [7][8][9].…”