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:
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.
Click individual topic for further information:
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
0.8 at% Yb, 0.8 at% Nd:GdVO4
3.0 at% Yb-0.7 at% Er YVO4
c-oriented 1.0 at% Nd:GdVO4
0.25 at.% Nd:LuVO4
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
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
Crystals for other applications
1. 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)
2. Crystals grown by Optical Floating Zone Technique.
Wide band gap material
(application: Transparent conducting oxide, solar blind photodetector, high voltage electronics)
Gallium oxide
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.
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.
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.
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.
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.
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.
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.
Effect of electric field induced structural ordering on photo-luminescence & piezoelectric response of Pr doped
(Na0.41K0.09Bi0.5)TiO3
Variation of d33, d31, kp, and k31; variation of remnant (Pr) & saturation (Ps) polarization; photoluminescence spectra of the unpoled and poled samples
The ferroelectric and photoluminescence response lacks one-to-one correlation.
Optimum ferroelectric response is observed for 1.0 at% Pr doping, whereas for higher doping concentration, it diminishes gradually due to disruption of the long-range ordering.
On the other hand, with the establishment of long-range ordering, no noticeable shift in the position and shape of the photoluminescence lines has been observed.
However, a quenching in the PL intensity of the hypersensitive transitions (1D2→3H4) takes place, which has been associated with the modification in the local site symmetry.
It has been argued that structural modification has an influence on the photoluminescence intensity but does not affect the energy levels of these transitions.
For details refer to:
J. Appl. Phys. 132, 224104 (2022)
Effect of Nb substitution on the electronic property of lead-free piezoelectric (Na0.41K0.09Bi0.5)TiO3 single crystal
Valence band spectra & ARPES band mapping showing non-bonding O 2pπ state
The optical bandgap is indirect in nature and increases with the increase in the Nb concentration in the lattice.
The estimated Urbach energy increases with the increase of Nb concentration signifying an increase in the disorder in the lattice on Nb doping.
The PES revealed that the valence band maxima (VBM) exhibit red shift on Nb doping.
It also revealed the presence of in-gap states probably due to Ti3+ defect and oxygen vacancy. Moreover, in-line with the optical measurement, the PES showed that there is a decrease in the energy gap between the VBM and defect state with the Nb doping.
For details refer to:
J. Appl. Phys. 132, 205103 (2022)
Structural evaluation in vicinity of composition induced nonergodic to ergodic crossover in niobium doped (Na0.41K0.09Bi0.5)TiO3
Evolution of XRD profile for (111), (200) and (220) reflection and micro-Raman spectra.
The diffraction studies reveal the co-existence of cubic (Pm3m), rhombohedral (R3c), and tetragonal (P4bm) phases for lower concentrations of niobium, i.e., for x ≤ 0.005 and the emergence of the pseudo-cubic (Pm3m) structure for higher niobium contents (for x ≥ 0.0075).
Raman spectroscopy reveals the augmentation of the tetragonal phase with Nb.
These observations advocate the crossover from the non-ergodic to ergodic phase with Nb content
The presence of the pseudo-cubic phase (Pm3m), especially for x ≥ 0.0075, does not indicate the existence of the long-range cubic phase; rather, it models the contribution of nano-regions with the tetragonal symmetry as indicated in the Raman measurements.
It further suggests that, with the incorporation of niobium, the size polar nano-regions diminish that leads to the crossover from the non-ergodic to ergodic phase.
For details refer to:
Journal of Applied Physics 134, 044105 (2023)
Optical properties and passive self Q-switching of floating zone grown Cr–Nd co-doped vanadate crystals
Passive Q switching at 1064 nm was demonstrated
For details refer to:
Optical Materials 152 (2024) 115500
Journal of Luminescence 263 (2023) 119973
Journal of Alloys and Compounds 886 (2021) 161182
Applied Physics A 125 (2019) 347
Elucidation of amphoteric nature of Pr2O3 using XPS and conductivity measurement in lead-free NKBT host lattice
Piezoelectric response in Pr-doped NKBT drastically diminishes for doping concentrations exceeding 1.0 at%.
The XPS study revealed that the concentration of the oxygen vacancy is lowest around 0.5 at% of praseodymium doping and beyond this the oxygen vacancy increases.
The high temperature conductivity measurement supported these findings by showing similar trends in the electrical conductivity.
Both the measurements corroborate the conjecture that Pr behaves as amphoteric ion. The Pr occupies the A-site for Pr <1.0 at%, whereas for Pr>1.0 at% it occupies the B-site exhibiting acceptor like behavior that deteriorates the piezo-response.
For details refer to:
Journal of Alloys and Compounds 1006 (2024) 176189
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.
Instruments and Measurement Set-up developed
Low temperature Solution growth workstation.
High temperature solution growth workstation.
Automatic diameter control (ADC) system (Czochralski crystal puller).
For the growth of crystals by conventional Bridgman technique (growth by moving the ampule) as well as vertical gradient freezing (VGF) technique (growth by changing the temperature gradient and keeping the ampule fixed) a five zone furnace is set up. To control the temperature of each zone individual single loop temperature controllers and thyristor are used. The temperature of all the zones was monitored using K-type thermocouple. Another set of ten thermocouple are used for on-line recording of the temperature profile along the entire length of the furnace using a chart-less recorder. All the temperature controllers and monitors are interfaced to PC using RS482-RS232 converter and the chart recorder was interfaced. The monitoring of control and data logging is performed using iTools software.
Five zone VGF/Bridgman growth set up. One of the optimized gradient freezing profile as a function of time.
A pyroelectric coefficient measurement set up has been developed in-house for the evaluation of pyroelectric properties of the crystals. In this method specimen is heated or cooled at a uniform rate, and the generated pyro-current is measured across a resistance. The generated pyro-voltage was recorded using high impedance Keithley make electrometer. A Kanthal make heating module was used to for heating the sample. A K-type thermocouple was used to monitor the sample temperature. The set can evaluate the pyroelectric coefficient from room temperature up to 600C. A lab view based PC interface was developed for data acquisation and logging.
The developed Pyroelectric measurement set up
Screen shot showing the temperature change and
generated pyrocurrent during the measurement
Comparison of pyroelectric coefficient of
undoped, Ce and Gd SBN-61 measured using the developed set-up
2. High temperature poling set-up (for ferroelectric domain switching):
Specifications:
Temperature range: up to 1200°C.
Current density range: 1-20 mA/cm2
High temperature poling set up comprising of in-house developed current source module
Softwares:
ADC control system for crystal growth.
Control and automation software for inhouse developed Czochralski puller.
Software for Dielectric measurement and data logging using Impedance analyzer (HP4194A Hewlett Packard, USA) .
Software rutine for calculating phase matching angle for different interactions in NLO crystals.
Devices developed
Several SHG elements and Electro-optic modulators have been fabricated and tested.
KDP Type-I SHG element has been fabricated for auto-correlation application.
SHG elements fabricated from KTP exhibit conversion efficiency of 60% (without accounting the Fresnel loss).
Lasing (1064 nm) has been demonstrated using Nd:YVO4 and Nd:GdVO4 single crystal.
Pyroelectricity based laser energy meter has been fabricated using lithium tantalate crystals.
IR windows (2 and 4 mm thick) have been fabricated using NaCl crystals.
1. Electro-optic (EO) modulator:
KDP EO modulator element; Size: 90 x 82 x 19 mm3; Half wave voltage: 9.1 kV (632 nm)
(001) KDP plate for EO modulator Size: 150 x 150 x 18 mm3
