The growth of novel and technologically important materials, especially in the form of single crystals, serves as the foundation stone for the scientific and technological developments of the human civilization. High-quality single crystals are an integral part of many new and existing technologies. Single crystals play a crucial role in this regard and are often required to achieve a material’s full functionality, as well as to completely describe its properties. Hence, over the years the growth and characterization of technologically important crystals have evolved as a thrust area in materials- science research.
There are different techniques employed for the growth of single crystals. Some of the important growth techniques are given below:
At LFMD several single crystals for laser-host, non-linear optical, ferroelectric and detector applications are grown using different growth techniques. Also crystal growth workstations with precision controls and high temperature stability have been designed and developed in-house. The grown crystals are characterised using characterization facilities available in the Division such as XRD, FTIR, DSC, TG-DTA, polarizing light microscope, optical interferometers, thermo-luminescence set up, hysteresis loop tracer, impedance analyzer etc. Several devices have been fabricated using the grown crystals.
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Non-linear optical crystals
Highlights:
Several non-linear optical crystals like Potassium di-hydrogen phosphate (KDP), Deuterated potassium dihydrogen phosphate (DKDP), stochiometric and congruent lithium niobate (LN) and lithium tantalate (LT), Potassium titanyl phosphate (KTP), borates etc. are grown by solution and melt growth techniques.
These crystal are grown for harmonic generation of laser output, electro-optic modulation applications.
KDP crystal of size 116 x 92 x 116 mm3 weighing 2.6 kg has been grown.
Large diameter lithium niobate (dia. 70 mm) and lithium tantalate (dia. 50 mm) crystals have been grown.
Several innovations like Mercury Seal Technique (to process solution with immersed seed), Flat-top Technique (to increase usable volume), Nucleation-trap Crystallizer (to trap spurious nucleation) for the growth of good quality crystals have been conceptualized and implemented.
Several SHG elements and Electro-optic modulators have been fabricated and tested.
1. Crystals grown by low temperature solution growth method
2. Crystals grown by high temperature solution growth method
β-Barium borate (BBO)
Cesium lithium borate (CLBO)
Stochiometric lithium niobate (SLN)
Mg:SLN
Potassium titanyl phosphate (KTP)
3. Crystals grown by Czochralski method
Congruent Lithium Niobate (CLN) crystals, wafers and elements
Zn, Co doped CLN crystals
Lithium Tantalate (LT)
Ru, Fe and Er doped CLN crystals
Mg doped CLN crystals
Laser crystals
Highlights:
Several rare earth doped ortho-vanadate crystals have been grown for application as laser gain medium.
Cr co-doped rare earth vanadates are grown for self Q-switching application.
1. Crystals grown by Optical Floating Zone Technique
Nd doped YVO4
Nd:Cr co-doped YVO4
Er doped YVO4
Nd doped GdVO4
Piezoelectric and ferroelectric crystals
Highlights:
Several lead-based and lead free ferroelectric crystals have been grown and investigated.
1. Crystals grown by Optical Floating Zone Technique
Sr0.61Ba0.39Nb2O6(SBN-61)
Gd doped Sr0.61Ba0.39Nb2O6
2. Crystals grown by high temperature slution growth Technique
PZN-PT crystals
PMN-PT crystals
BCT-BZT crystals
NBT-KBT crystals
Crystals for other applications
1. Crystals grown by low temperature solution growth.
X-ray monochromator
As-grown AAP crystal size: 120 x 42 x 90 mm3
As-grown KAP crystal size: 78 x 46 x 75 mm3
2. Crystals grown by Czochralski method.
Scintillators
Lead Tungstate (PbWO4)
Lead Tungstate (PbWO4)
Undoped Bismuth Silicate (BSO)
Ce doped Bismuth Silicate (BSO)
IR window material
Sodium Chloride (NaCl)
3. Crystals grown by Optical Floating Zone Technique.
Wide band gap material
(application: Transparent conducting oxide, solar blind photodetector, high voltage electronics)
Gallium oxide
Multi-ferroic materials
Besides scientific interest in their physical properties, multiferroics have potential for applications as actuators, switches, magnetic field sensors and new types of electronic memory devices.
LaMnO3
YMnO3
GdFeO3
SmFeO3
GaFeO3
YFeO3
Investigations on single crystals
1. investigations on piezoelectric crystals
(a) Domains observed in BCT-BZT under PLM (Mag.: 5x);
(b) Temperature dependent PLM image of BCT-BZT during heating and cooling;
(c) Temperature dependent dielectric constant and tand for (001) BCT-BZT;
(d) Electro-caloric temperature change at different electric field for BCT-BZT; (e) P-E hysteresis loops for NKBT.
For details refer to:
J. Crystal Growth, 375 (2013) 20.
Applied Physics Letters, 102 (2013) 082902.
Materials Science and Engineering B 185 (2014) 60.
Materials Science and Engineering B 185 (2014) 134.
Materials Research Bulletin 53 (2014) 136.
2. Investigations on undoped and doped Gallium oxide crystal
(a) Rocking curve of (004) peak of undoped and Sn doped Ga2O3 sample (shift is due to lattice expansion in Sn doped crystal);
(b) Optical transmission spectra (the crystal grown in 5% oxygen exhibits broad absorption at wavelength);
(c) Temperature dependent PL spectra;
(d) Effect of Al doping on the lattice volume and optical band gap;
(e) Refractive index and Sellmeier fitting of undoped β-Ga2O3.
For details refer to:
Applied Optics, 50 (2011) 6006.
Optical Materials 109 (2020) 110351.
3. Unusual absorption and emission characteristics of Cr co−doped Nd:GdVO4 laser gain crystal
π-Polarized absorption spectra for low and high Cr concentration in the Nd:GdVO4
grown in different ambience.
For details refer to:
J. Alloys and Compounds 886 (2021) 161182.
4. Investigation of optical and spectroscopic properties of Nd co-doped Yb:YVO4 single crystals
Absorption spectra of Nd co-doped Yb:YVO4 crystal for π-polarization PL intensity of Nd:Yb:YVO4 with excitation 808 nm
For details refer to:
J. Luminescence 231 (2021) 117736.
5. Spectroscopic properties and Judd-Ofelt analysis of Nd doped GdVO4 single crystals
Relative PL intensity of Nd:GdVO4 with excitation 808 nm; Fluorescence decay of Nd 0.6 at.% doped GdVO4 crystal
For details refer to:
Opt. Materials 92 (2019) 379.
6. Effect of oxygen partial pressure on the oxidation state of chromium in Nd:Cr:YVO4 single crystals
Absorption spectrum of the crystals grown in different oxygen atmospheres, namely, air, 25%, 75%, and 100% oxygen. Inset: Comparison for 2A1→ 2B2 transition.
For details refer to:
Cryst. Growth Des., 13 (2013) 3878.
7. Bipolar electro-caloric effect (ECE) in SrxBa(1−x)Nb2O6 lead-free ferroelectric single crystal
Electro-caloric temperature change (ΔT) as a function of temperature at different applied electric fields for (a) 75SBN (x=0.75), (b) 61SBN (x=0.61) and (c) 50SBN (x=0.5). Region-I and region-II indicate negative and positive ECE, respectively.
For details refer to:
Europhysics Letters, 107 (2014) 47001.
Innovations for crystal growth techniques
Several innovations like Mercury Seal Technique (to process solution with immersed seed), Flat-top Technique (to increase usable volume), Nucleation-trap Crystallizer (to trap spurious nucleation) for the growth of good quality crystals have been conceptualized and implemented.
A novel seeding technique has been developed which helps in the quick establishment of the growth temperature with minimum wastage of seed.
1. Mercury seal technique (to process solution with immersed seed)
Schematic of the growth assembly
For details refer to:
J. Crystal Growth, 289 (2006) 617.
2. Flat-top technique (to increase usable volume)
Schematic of Flat-top technique, obtained crystals and elements
For details refer to:
Optical Materials 46 (2015) 329.
For details refer to:
J. Crystal Growth 297 (2006) 152.
4. Novel seeding technique
Details of the seeding process. (a) The seed tip touches the top of the molten solution.
(b) The seed is pulled up, but is still in contact with the solution due to surface tension
For details refer to:
J. Crystal Growth, 243 (2002) 522.
