5.2 Growing the crystal

L1 Phenomenon

Commercial LN is grown by the Czochralski method: a seed crystal touches the surface of the melt in a crucible, is rotated slowly and pulled upward by one or two millimetres per hour, and the crystal grows from the meniscus. A 150 mm (6-inch) boule takes days to grow. The melt is not LiNbO₃ of formula composition but the congruent composition, slightly short of lithium, because only that melt freezes to a solid of the same composition from top to bottom.

Czochralski growth and compositionbody: cylinder 153 mm × L

(a) side profile, 1 col = 5 mm, 1 row = 10 mm

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Time t 55.0 h

Pull rate

1.5 mm/h

Rotation 7.5 rpm

L 82.5 mmt 55.0 hm 7.05 kgturns 24750derived

(b) Curie temperature vs crystal composition

Composition c48.45 mol%

T_c Bordui 1145.9 °CT_c Iyi 1141.5 °CP-comp

Congruent range: the melt freezes to a solid of the same composition, uniform from seed to tail.

Points: P-comp CLN 1140 °C (Volk); V 1142.3 °C at 48.38 mol%; near-SLN 1206 °C P-comp vs 1213 °C S, a conflict. Growth inputs S. Crucible, afterheater, 45° shoulder and seed along Z: template

Growth time55.0 h

Pull rate (reported 1 to 2 mm/h)

Rotation (reported 5 to 10 rpm)7.5 rpm

Body length: 82.5 mm
Body mass: 7.05 kg
Turns so far: 24750

Inputs S; L = v t and mass derived. Crucible, afterheater, 45° shoulder and a seed along Z are drawing values template.

Crystal composition48.45 mol%

T_c, Bordui 1992: 1145.9 °C
T_c, Iyi 1992: 1141.5 °C

Congruent range: the melt freezes to a solid of the same composition, uniform from seed to tail. P-comp

Dots under the axis: reported T_c: CLN 1140 °C P-comp, 1142.3 °C at 48.38 mol% V; near-SLN 1206 °C vs 1213 °C, a conflict P-comp S.

Process viewer stepsopen in the Process viewer

#	STEP	ROUTE
02	Melt the charge	ridge
03	Czochralski growth (seed, neck, shoulder, body, tail)	ridge
04	Anneal and pole the boule to a single domain	ridge

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Step progress t0.70

Step

Step progress0.70

3/23Czochralski growth (seed, neck, shoulder, body, tail) (ridge route)

L2 Model and data

Composition and phase behaviour

Quantity	Value	Source; status
Liquidus maximum (congruent melt)	near 48.6 mol% Li₂O	P-comp
Congruent composition	48.45 mol% Li₂O; [Li]/[Nb] = 0.94	P-comp
Congruent composition, vendor value	48.38 ± 0.01 mol%	V
Congruent vs near-stoichiometric (mole fraction Li₂O)	0.484 vs 0.498	P(abs)
Melting point, CLN	1255 °C (compilation); about 1250 °C (vendor)	P-comp, V
Curie temperature, CLN	1140 °C (Volk); 1142.3 ± 0.7 °C at 48.38 mol% (vendor)	P-comp, V
Curie temperature, near-SLN	1206 °C (Volk) vs 1213 °C (secondary): conflict	P-comp, S
T_c vs crystal composition c (mol% Li₂O)	T_c = 39.064 c - 746.73 (Bordui 1992); T_c = 39.26 c - 760.67 (Iyi 1992)	P-comp
T_c from the Bordui fit at 48.38 / 48.45 / 50.0 mol%	1143.2 / 1145.9 / 1206.5 °C	derived

Czochralski growth parameters reported for LN (re-keyed from the table in S; originals cited there)

Pull rate (mm/h)	Rotation (rpm)	Crystal diameter x length (mm)	Li content spread (unit as printed: mol%/cm)	Original
1-2	5-10	153 × 110	delta[Li₂O] about 0.001	S
2.8-4.0	3-10	100 × 80	delta[Li₂O] < 0.002	ref. 22 of S
1-2.5	10-25	80 × 60	delta[Li₂O] < 0.02	ref. 30 of S
0.4-1.5	10-30	50 × 30	delta[Li₂O] < 0.005	ref. 29 of S

The 153 mm boule grown at 1-2 mm/h and 5-10 rpm showed a Curie-temperature deviation of at most 1.3 °C across the crystal S. Its body (110 mm) therefore takes 55 to 110 h to pull (derived: length / rate; shoulder, tail, and cool-down excluded). Body mass about 9.4 kg (derived: cylinder 153 mm × 110 mm, 4647 kg/m³).
First Western report of Czochralski-grown LN: Ballman, J. Am. Ceram. Soc. 1965 P(title).
Crucible material, atmosphere, afterheater design, and seed orientation used for production boules: not found in a primary source as of 2026-10-25. The growth figure draws them as labelled template values.

Routes to near-stoichiometric LN (SLN)

Route	What the source states	Source; status
Double-crucible Czochralski with automatic powder supply	Growth of stoichiometric LiNbO₃ single crystals by a double-crucible Cz method with an automatic powder supply system	P(title)
Vapour transport equilibration (VTE)	Off-congruent crystals prepared by VTE; T_c and noncritical phase-matching temperature nearly linear in Li/Nb; crystals equilibrated to the Li-rich phase boundary had excellent optical homogeneity; Li-poor preparation hampered by very slow Li diffusivity and second-phase precipitation	P(abs)
Why SLN matters for making things	Switching (coercive) field ratio CLN / near-SLN 4-5; internal field about 2.5 kV/mm in CLN, vanishing in SLN	P(abs)
Coercive field, literature averages	CLN 21 kV/mm; SLN 6.0-6.5 kV/mm; 5% MgO:CLN 6.0-6.8 kV/mm (individual reports 2.5-4.5 kV/mm)	P-comp; p. 118 of the same compilation gives 2.1-2.5 kV/mm for near-SLN P-comp

MgO doping

Quantity	Value	Source; status
Threshold for damage resistance, congruent	4.5 at.% MgO or more; photoconductivity up 100x; Glass current not reduced; activation energy 0.1 eV vs 0.5 eV; OH line moves from 2.87 to 2.83 µm	P(abs)
Priority	Zhong, Jin, Wu, IQEC 1980 conference abstract; journal report Bryan 1984	P(title), P(abs)
Near-stoichiometric MgO:SLN threshold	above 0.78 mol% MgO, no damage at 532 nm to 2 MW/cm²	P(abs)

Single-domain boules

Nassau, Levinstein, and Loiacono reported the domain structure of LN crystals revealed by etching (1965) P(title) and the preparation of single-domain crystals (1966) P(title).
The procedure (field applied while the boule cools through T_c; electrode and field values) is not quoted here because the paper body was not read. The Process viewer draws boule poling with template values and a U badge on the procedure.

L3 Details and open points

Lineage: congruent Li-deficiency of commercial crystals P(title); congruent melt for uniform boules P(title).
Composition is measured indirectly: Curie temperature (linear in Li/[Li+Nb]), UV absorption edge, Raman line widths S. T_c fits by Bordui and Iyi differ by 4.5 °C at 48.38 mol% (derived from the fits above); the SLN T_c of 1213 °C sits above both fits at 50.0 mol% (derived from the fits above).
P_s differs between sources: 80 ± 5 µC/cm² P(abs) vs 71 (CLN) and 62 (near-SLN) µC/cm² P-comp.
Thermal expansion along c disagrees across sources (4.1 to 7.5 ppm/K); Volk gives α_a = 14.1 × 10⁻⁶ /K and α_c = 4.1 × 10⁻⁶ /K for CLN at 300 K P-comp. The anisotropy matters for boule cracking and for bonding to Si (5.5).
The growth table above mixes congruent and doped crystals from different groups; it shows ranges, not one recipe.

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