Effects of Hydrostatic Pressure on the I–II Phase Transition in an Improper Ferroelectric NH₄LiSO₄

Study on the structural properties and relaxation mechanisms in LiRb1−x(NH4)xSO4 (x=0, 0.5, and 1) mixed crystals by 1H, 7Li, and 87Rb nuclear magnetic resonance

“…The spin-lattice relaxation times of the 1 H, 7 Li, and 87 Rb nuclei in the LiRb 1À x (NH 4 ) x SO 4 (x¼0, 0.5, and 1) single crystals were measured using the Bruker MSL 200 FT NMR and Bruker DSX 400 FT NMR spectrometers at the Korea Basic Science Institute. The static magnetic fields were 4.7 and 9.4 T, respectively, and the central radio frequencies were set at o H /2p¼200 MHz for the 1 H nucleus, o Li /2p¼155.51 MHz for the 7 Li nucleus, and o Rb /2p¼130.92 MHz for the 87 Rb nucleus.…”

“…When a fraction of rubidium ions in the pure LiRbSO 4 crystal is partially replaced by ammonium ions, we compare the structural properties for LiRbSO 4 , LiRb 0.5 (NH 4 ) 0.5 SO 4 , and LiNH 4 SO 4 single crystals. The 1 H, 7 Li, and 87 Rb NMR relaxation mechanisms of LiRb 0.5 (NH 4 ) 0.5 SO 4 are different from those of pure LiRbSO 4 and LiNH 4 SO 4 ; the sequence of the structural phase transitions of LiRb 0.5 (NH 4 ) 0.5 SO 4 is different, which might be related to the dynamics and orientation of the sulfate tetrahedral groups in the crystal structure.…”

“…A large number of studies have examined the properties of the different phases of LiNH 4 SO 4 , with the ferroelectric behavior of the room temperature phase attracting particular attention. LiNH 4 SO 4 is an extremely interesting material that undergoes four phase transitions, at 459.5 K ( ¼T C1 ), 284.5 K ( ¼T C2 ), 133 K (¼ T C3 ), and 27 K ( ¼T C4 ) [6][7][8][9]. These four transitions of LiNH 4 SO 4 single crystals separate five phases denoted by I, II, III, IV, and V in order of decreasing temperature.…”

“…Further, this study examined the effects of the random presence of electronically different cations of similar size. To probe the structural properties of the three single crystals, LiRbSO 4 , LiRb 0.5 (NH 4 ) 0.5 SO 4 , and LiNH 4 SO 4 , the measurement of the 1 H, 7 Li, and 87 Rb relaxation times was preferred, because these relaxation times are likely be very sensitive to changes in the symmetry of these crystals. The nuclear magnetic resonance (NMR) spectrum and spin-lattice relaxation times, T 1 , for 1 H, 7 Li, and 87 Rb in LiRbSO 4 , LiRb 0.5 (NH 4 ) 0.5 SO 4 , and LiNH 4 SO 4 single crystals were obtained.…”

Structural properties in mixed LiK1−(NH4) SO4 (x= 0, 0.06, and 1) crystals by nuclear magnetic resonance

“…Several studies have examined the properties of the different phases of LiNH 4 SO 4 , with the ferroelectric behavior of the room-temperature phase attracting particular attention. LiNH 4 SO 4 undergoes four phase transitions, at 459.5 K (=T C1 ), 284.5 K (=T C2 ), 133 K (=T C3 ), and 27 K (=T C4 ) [11][12][13][14]; these four transitions separate five phases, denoted as I, II, III, IV, and V (in order of decreasing temperature). The symmetry of the high-temperature phase above 459 K has been identified as orthorhombic Pmcn (mmm).…”