lithium niobateLiNbO3
PPLN Λ = 6.82 µm · 1064 → 532 nm · 2 px/µm
lithium niobate / 01 Crystal / 1.3

1.3 Ferroelectric constants

L1 Polarization to 1140 °C

Volk & Wöhlecke 2008 Table 1.1

LiNbO3 keeps its polarization up to about 1140 °C in the usual congruent crystal and about 1206 °C in near-stoichiometric crystal; congruent crystal melts at 1255 °C, only 115 degrees higher P-comp. That high Curie temperature makes the polarization of a commercial wafer permanent for practical purposes: no device processing step comes close.

Temperature axis: Tc(c) from two fits, Tc and Tm markersP-comp derived
48.45 mol%
1142.3 °C
1100–1300 °C, 5 °C per character= ferroelectric  # between fits  ^ marker  | input
T / °C    1100      1150      1200      1250      1300
          |----+----|----+----|----+----|----+----|
c 48.45   ========##-------------------------------
Tc CLN            ^
Tc nSLN                        ^
Tm CLN                                   ^
Tc input          |
Tc(c), Iyi fit1141.5 °Cderived
Tc(c), Bordui fit1145.9 °Cderived
1255 °C − Tc(c)109–114 °Cderived
c(Tc input), Iyi48.47 mol%derived
c(Tc input), Bordui48.36 mol%derived
Difference0.11 mol%derived
Composition → temperature: move c; the Tc band shifts 39 °C per mol%. Temperature → composition: set a measured Tc (default 1142.3 °C, vendor value for 48.38 mol% V); each fit returns a composition. Markers: P-comp; near-stoichiometric melting point not drawn P-comp.
48.45 mol%
1142.3 °C
Tc(c), Iyi fit derived
1141.5 °C
Tc(c), Bordui fit
1145.9 °C
Margin to 1255 °C derived
109–114 °C
c from Tc, Iyi fit derived
48.47 mol%
c from Tc, Bordui fit
48.36 mol%
Fits disagree by
0.11 mol%

Stripes: ferroelectric phase, ±z domains possible; green band: Tc between the two fits at the chosen c. Waves: congruent crystal molten above 1255 °C. The solid line is the measured Tc; default 1142.3 °C, the vendor value for 48.38 mol% V. Markers P-comp; near-stoichiometric melting point not drawn P-comp.

L2 Ps, Tc, melting

room temperature unless stated
QuantityCongruentNear-stoichiometricStatus
Ps, room temperature conflict71 µC/cm2 = 0.71 C/m2printed 62 µC/cm2; the cited source is on LiTaO3 (L3), not an LN valueP-comp
Ps, P–E loop conflict71 µC/cm2; “experimental 0.71 C/m2”–P-comp P(abs)
Ps, P–E loop conflict80 ± 5 µC/cm2 = 0.80 C/m2same; “relatively insensitive” to stoichiometry and hydrogenP(abs)
Curie temperature Tc1140 °C1206 °CP-comp
Tc, 48.38 mol% Li2O1142.3 ± 0.7 °C–V
Tc in Weis & Gaylord 1985“approximately 1210 °C” in the text; 1165 °C for one listed sample; internally inconsistent–P
Melting point Tm1255 °Cnot shown: the printed value lies below the 1206 °C Tc of the same table impossibleP-comp
Pyroelectric signp3 < 0: on cooling the +c face becomes more positive–P

Ps: two measured values, 0.71 and 0.80 C/m2; where one number is needed this chapter computes with 0.71 C/m2 conflict.

Tc as a composition gauge

c = Li2O content of the crystal, mol%; Tc in °C:

Tc = 39.26 c − 760.67     (DTA, 4 crystals, chemical analysis)   P-comp
Tc = 39.064 c − 746.73    (dielectric, 5 VTE crystals)           P-comp
c (mol% Li2O)Tc, Iyi fitTc, Bordui fitStatus
48.381138.7 °C1143.2 °Cderived
48.451141.5 °C1145.9 °Cderived
49.001163.1 °C1167.4 °Cderived
50.001202.3 °C1206.5 °Cderived

Slope: 39 °C per mol% Li2O; across the room-temperature solid-solution range Tc changes by about 150 °C P-comp.

L3 How Tc is measured

DTA, dielectric peak; Ps disagreement

Methods. Tc is measured by differential thermal analysis or by the dielectric peak; its closeness to the melting point is the method's drawback P-comp. Weis and Gaylord call Tc “a very reliable and accurate indicator” of composition P. The two fits differ by 4 °C, i.e. 0.1 mol% P-comp. A neutron study puts Tc near 1430 K for an unstated composition P(abs). Above Tc the crystal is in its paraelectric phase.

Disagreement on Ps. Reported values span 62 to 85 µC/cm2. For the Ps column of its Table 1.1, Volk & Wöhlecke 2008 cites a 1998 APL paper whose Crossref title concerns stoichiometric LiTaO3 P, so the 62 µC/cm2 near-stoichiometric entry has no LN source on record. Gopalan et al. 1998, measured on both compositions, reports 80 ± 5 µC/cm2 and no composition dependence P(abs). Ps is therefore given as 0.71–0.80 C/m2 with both sources conflict.

Tc in Weis & Gaylord 1985. The review gives “approximately 1210 °C” in its text and 1165 °C for one sample in its Table 1, for crystals of unstated composition P; neither is used as a headline value. Through the fits, 1165 °C corresponds to about 49.0 mol%, 1210 °C lies above 50 mol% derived.

Melting point of near-stoichiometric crystal. The value printed in Volk & Wöhlecke 2008 Table 1.1 lies below the near-stoichiometric Tc of the same table, which is physically impossible; it is not shown, and no other source for it is held P-comp.

Sources

9 cited in 1.3
  1. Volk & Wöhlecke 2008T. Volk, M. Woehlecke, Lithium Niobate: Defects, Photorefraction and Ferroelectric Switching, Springer Series in Materials Science 115 (Springer, Berlin Heidelberg, 2008). doi:10.1007/978-3-540-70766-0
  2. Crystal Technology 1999Crystal Technology Inc., "LiNbO3 material properties", data sheet DC-12 8/99 (congruent, 48.38 mol% Li2O).
  3. Hsu et al. 1997R. Hsu, E. N. Maslen, D. du Boulay, N. Ishizawa, "Synchrotron X-ray studies of LiNbO3 and LiTaO3", Acta Cryst. B 53, 420-428 (1997). doi:10.1107/S010876819600777X
  4. Gopalan et al. 1998V. Gopalan, T. E. Mitchell, Y. Furukawa, K. Kitamura, "The role of nonstoichiometry in 180 ° domain switching of LiNbO3 crystals", Appl. Phys. Lett. 72, 1981-1983 (1998). doi:10.1063/1.121491
  5. Kitamura et al. 1998K. Kitamura, Y. Furukawa, K. Niwa, V. Gopalan, T. E. Mitchell, "Crystal growth and low coercive field 180 ° domain switching characteristics of stoichiometric LiTaO3", Appl. Phys. Lett. 73, 3073-3075 (1998). doi:10.1063/1.122676
  6. Weis & Gaylord 1985R. S. Weis, T. K. Gaylord, "Lithium niobate: Summary of physical properties and crystal structure", Appl. Phys. A 37, 191-203 (1985). doi:10.1007/BF00614817
  7. Iyi et al. 1992N. Iyi, K. Kitamura, F. Izumi, J. K. Yamamoto, T. Hayashi, H. Asano, S. Kimura, "Comparative study of defect structures in lithium niobate with different compositions", J. Solid State Chem. 101, 340-352 (1992). doi:10.1016/0022-4596(92)90189-3
  8. Bordui et al. 1992P. F. Bordui, R. G. Norwood, D. H. Jundt, M. M. Fejer, "Preparation and characterization of off-congruent lithium niobate crystals", J. Appl. Phys. 71, 875-879 (1992). doi:10.1063/1.351308
  9. Boysen & Altorfer 1994H. Boysen, F. Altorfer, "A neutron powder investigation of the high-temperature structure and phase transition in LiNbO3", Acta Cryst. B 50, 405-414 (1994). doi:10.1107/S0108768193012820