Ceramic Activity

Objective:

Research and development on technologically important ceramic materials for specialized applications viz. lasers, scintillators and piezoelectricity forms an important activity of the division. As part of the ceramic activity technologically important materials for these specialized application are being pursued in area of Transparent Ceramics, Electro-ceramics and Multiferroics.

Considerable effort has been put in to in-house fabricated/synthesized following technologically important ceramic material:

  • Transparent ceramics for laser host, IR windows, Electro-optic and scintillator applications.
  • Ferro-electric, piezo-electric and multi-ferroic materials.

Applications:

Click below for further information:

Transparent ceramics for laser host application:

  • Materials fabricated: Nd:YAG, Yb:YAG and Nd:Y2O3.
  • Dimensions: Diameter= 13 mm; Thickness = 1 mm.
  • Fabrication method: Nano powder synthesis, compaction and sintering.
  • Properties:

    • Absorption and photoluminescence: Comparable to reported results.
    • Transparency: 75-79% (without Fresnel loss correction) at 1000 nm. Further optimization to reduce the residual porosity with the help of HIP is underway to acheive the targeted transparency of 84%.

Transparent ceramics for Scintillator application:

  • Materials fabricated: Ce:YAG (Optimum Ce concentration: 0.1-0.2 mol%).
  • Dimensions: Diameter= 30 mm; Thickness = 0.5 mm.
  • Fabrication method: Nano powder synthesis, compaction and sintering.
  • Properties:

    • Absorption and photoluminescence: Comparable to reported results.
    • Transparency: 75% (without Fresnel loss correction) at 1000 nm.

  • Successfully tested for:

    • X-ray imaging using laboratory as well as synchrotron (INDUS-2) X-ray source with spatial resolution of ~20 μm.
    • Detection of electron beam (energy: 5 - 35 keV; current: 10 to 46 mA) and hydrogen negative ion.
    • Generated white light using partial conversion method in Ce:YAG of different thickness.

Transparent ceramic for IR window application:

Monolithic growth of free-standing ZnS blanks and domes are fabricated using sub-atmospheric pressure chemical vapour deposition (CVD). Optical properties are consistent with the ealier reports. Yellow coloration in the ceramics are due to trapping of sulfur. This material is used as IR-window to protect thermal imaging equipment for strategic application

  • Materials fabricated: Monolithic Zinc Sulfide (ZnS).
  • Dimensions: (i) Blank, Diameter= 80 mm; Thickness = 2.0 mm
                        (ii) Dome, Rim Diameter = 80 mm, Thickness = 2.0 mm.
  • Fabrication method: Chemical Vapour Deposition (CVD).
  • Properties:
    • Phase: Cubic crystal symmetry with lattice parameters 5.405 Ao.
    • Transparency: 65–68 % transmission in the 8–12 μm wavelength region.
    • Vicker’s Hardness: 175 – 200 (with 50 gm applied load).
    • Density: 4.09 gm/cc.

Transparent ceramic for Electro-optic application:

  • Materials fabricated: PLZT and Nd or Yb doped PLZT.
  • Dimensions:Plate, Length and Width 5-10 mm; Thickness = 2.0 mm.
  • Fabrication method: Hot pressing of PLZT powder.
  • Properties:
    • Phase: Pseudo-cubic crystal symmetry.
    • Transparency: 40-50 % transmission at ~ 1 μm wavelength.
    • Application: Half-wave voltage, measured for He-Ne laser light, is only 200 V, compared to ~8 kV for a crystal of KDP.

Relaxor Ferroelectrics:

Relaxor ferroelectrics (RFEs) belong to a special class of ferroelectric materials, which have attracted incredible attention of scientific community for the last half century due to their extraordinary dielectric, piezoelectric, electromechanical, electro-caloric, and pyroelectric properties, which make it technological important materials for piezoelectric/electrostrictive actuators, sensors, and as electro-optic and photorefractive elements. Number of relaxor materials are fabricated using solid state route and their structure property correlations are established.


Material Investigated: Lead Magnesium Niobate (PMN)
  • Unsolved Issues: It was not clear (i) at what temperature the chemical ordered regions (CORs) appeare and how the size of the CORs corrrelate with the sintering temperature and polar nano regions (PNRs).
  • Issues solved: Present investigation concluded that the CORs are formed as soon as perovskite phase is formed during calcination becuase:
    1. Presence of (½½½) superlattice reflections along <111> in <110> zone axis SAED pattern, in 800 oC hot pressed PMN.
    2. Size of the CORs remain invariant with increasing sintering temperature.
    3. Increase in the εm from 8000 to 25000 (shifting of the Tm from 278 K to 263 K).
    4. Increase in the Pmax from 9 to ~17 μC/cm2, implies increase in the size of PNRs and their co-operative interaction.
Material Investigated: Lead Magnesium Niobate (PMN)-lead zirconate / lead titanate solid solution.
  • Unsolved Issues: Mechanism of relaxation and relaxor to normal-ferroelectric transformation and shape memory effect was not reported
  • Issues solved:
    1. A cross-over from relaxor to normal ferroelectric transformation in the composition range 0.42 < x < 0.46, where the piezoelectric (d33) and electromechanical (k31) coefficients were maximum.
    2. Shape-memory strain in thin bars of PMN-PT ceramic for compositions near its morphotropic phase-boundary.
    3. Maximum pseudo-plastic strain measured was ~ 0.3% in 65/35 PMN-PT.

2. Lead free environment friendly ceramics:


2.1 Material Investigated: Sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) and modified barium titanate
  • Unsolved Issues: Structure property correlation.
  • Issues solved:
    1. Piezoelectric and electro-caloric coefficients were enhanced by nearly 30 and 50% for optimum Ca content of 8 mol%.
    2. A 20-25% increase in the piezoelectric properties of (Na0.41K0.09 Bi0.5)TiO3 with 0.5 at% doping of Nb+5 ion.
    3. Temperature dependent dielectric properties in alio-valent substituted barium titanate (Ba1-yKyTi1-xNbxO3) compositions (x = y = 0, 0.05, 0.075 and 0.15)
      has revealed
      (a) change in ferroelectric behavior to typical relaxor behavior and
      (b) maximum ~ 0.06% electrostriction strain with almost no hysteresis loss.

3. Multiferroics:

Recently, magnetic ion (transition metals or rare-earths) doping in ferroelectric ceramics is being investigated intensely in order to add new functionality namely magnetism to make it multiferroics. The multiferroics are single phase compounds or multiphase composites, which possesses simultaneously two or more primary ferroic orders viz. ferroelectric, ferromagnetic and ferroelastic. At present, multiferroic materials are gaining lot of attention due to its technological importance and scientific challenges as magnetism and ferroelectricity are two independent phenomena.


3.1 Material Investigated: Gd-doped PMN and lead cobalt niobate ceramic (PCN).
  • Unsolved Issues: How magnetism develop in these ceramics was not known.
  • Issues solved: Gd-substituted PMN Pb1-xGdx(Mg1+x/3Nb2-x/3)O3 (0 ≤ x ≤ 0.1) ceramics has revealed:
    1. Segregation of second GdNbO4 and MgO phases for x ≥ 0.05.
    2. Enhancement in size of the CORs and reduction in size of PNRs.
    3. Critical slowing down of PNRs ensemble resulting to a super-dipolar glass state.
    4. Temperature and field induced magnetization M(T/H) investigations revealed paramagnetic behaviour.
    5. Magnetization and magnetodielectric (MD) study has revealed few very small sized correlated regions where Gd-ions are present at the A-site and B-site in the same lattice.
    6. Re-enterant relaxor behavior is observed in PCN due to development of weak anti-ferromagnetic correlations around 150 K in PCN.