Furnaces and growth techniques

Materials and Methods at the Laboratory for Materials Processing and Crystal Growth (LCG)



Travelling Solvent Floating Zone

In the Travelling Solvent Floating Zone (TSFZ) the molten precursors are kept at a fixed position in the composition-temperature phase diagram, thus creating a steady-state during which a crystal of given composition grows from a small liquid volume with a different composition, constantly fed by the precursors. This technique proved to be the most suitable, and often the only possible, for growing crystals of transition metal oxides and in particular superconducting cuprates. Non-congruently melting materials can be successfully grown by the TSFZ technique. At LCG there are two mirror furnaces available for the TSFZ growth: 1 commercial 2-lamp furnace, 10-8 bar < P <10 bar, either inert, or oxidising or reducing atmosphere, T<2200°C; and 1 home-made 2-lamp furnace, 10-6 bar < P <3 bar, under either inert, oxidising or reducing atmosphere, T<1200°C.

 

2-mirrors commercial optical furnace for TSFZ.
2-mirrors home-made optical furnace for TSFZ.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Materials grown by the Travelling Solvent Floating Zone in the optical (“mirror”) furnace:
Bi2Sr2CuO6
Bi2Sr2CaCu2O8
Bi2Sr2Ca2Cu3O10
Bi2Sr2(Ca,Ln)Cu2O8+x (Ln=Y, Pr)
(Ca,Sr)14Cu24O41
CuO
LiCu2O2
Dy:(Sr,Eu)Al2O4
Bi2Se3
Bi2(Se,Te)3
Bi1-xSbx
Fe(Te,Se)

 

 

 

 

Crystal of superconducting Bi2Sr2Ca2Cu3O10 (Tc = 110 K) grown by the TSFZ method.
Growth of CuO by the TSFZ in the mirror furnace.

 

Crystal of CuO grown by the TSFZ.

 


Chemical Vapour Transport

In the Chemical Vapour Transport (CVT) growth method, a volatile substance, in most cases a halogen or a halide compound, is added to the mixture of the raw materials in order to transform the non-volatile metal into some molecular species that permit its diffusion in the atmosphere. As soon as the partial pressure is high enough, the crystallization can occur in the cold part of the reaction ampule. This growth technique is commonly realized in closed reactors placed in a controlled temperature gradient. Various single-zone and multi-zone tubular furnaces are available for the CVT growth process.

 

Five-zone tubular furnace, maximum T 1100°C, controlled atmosphere.
Three-zone tubular furnace, maximum T 1450°C, controlled atmosphere.
Single-zone tubular furnace, maximum T 1100°C, controlled atmosphere.

 

Materials grown by the Chemical Vapour Transport in sealed quartz reactors:
Transition Metal Di-chalcogenides MX2 (M=Ti,Zr,Hf,V,Nb,Ta,Mo,W  X=S,Se,Te)
Topological Insulators: Bi2Se3, BiTeI
Oxides: CuO
Pnictides: SiP, GeAs

 

Crystals of TiSe2 grown at the cold end inside the quartz reactor.

 

Crystals of various Transition Metal di-Tellurides grown by the CVT.

 


High-pressure melt-growth

High isostatic pressure in the GPa range can favour the growth of metastable materials, as well as materials containing highly volatile, toxic and unstable components. The high isostatic pressure is applied mechanically onto small rectors that can be heated to the reaction temperature. The laboratory is equipped with a cubic-anvil hot press working up to a maximum pressure of 10 GPa and a maximum temperature of ~1500°C.

 

Pressure cell and sample in the cubic-anvil assembly.
500 tons press for the cubic-anvil HP furnace.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Materials grown at high pressure in the cubic-anvil hot press:
MgB2
Pnictdes: SiP, GeP, SIAs, GeAs

 

Crystals of GeP (left), GeAs (middle). Layered micaceous structure of GeAs (right).

 


Czochralski growth from melt

In the “Czochralski” growth method, the feed material is melted in a crucible heated by either resistive or inductive heaters. By dipping a crystal seed in the liquid surface of the melt, the crystal nucleates, and then grows by slowly pulling (and rotating) upwards the seed. This technique has become the most widely used for the industrial production of bulk crystal growth of semiconductors and optical crystals.

In special cases it is possible to make the molten precursors levitate in a magnetic field, thus preventing the feed from any possible contamination prior to crystallization. The LCG is equipped with two kinds of radio-frequency inductive furnaces for Czochralki growth: one operating by heating the metallic crucible (Pt, Ir, Mo or W) containing the precursor material, the other operating by directly melting the metallic precursor material in a Hukin-type cold crucible in which the molten precursor levitates.

 

Induction furnace for Czochralski growth.
Czochralski growth of (Fe,Co)Si from levitating melt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Materials grown by Czochalski pulling from levitating melt:

Transition Metal Silicides MnSi, CoSi, FeSi, NiSi and their solid solutions

 

 

As-grown crystal of (Fe,Co)Si.

Réalisation: Sur Mesure concept