Research & Development in the area of Cryogenics & Superconductivity at National Physical Laboratory, New Delhi

HARI KISHANhkishan@mail.nplindia.ernet.in

11th April 2006

CONTRIBUTORS• Dr. K.G. Ramanathan• Dr. M.S.R. Chari• Dr. J.S. Dhillon• Mr. R. Sundram• Dr. V.G. Bhide• Mr. Y.S. Reddy• Dr. N.S. Natarajan• (Late) Dr. V.S. Tomar• (Late) Dr. N.D. Kataria• Mr. S.C. Gera• Dr. A.V. Narlikar• Dr. Ashok Gupta• Dr. A.P. Jain• Dr. Neeraj Khare• Mr. Kasturi Lal• Mr. N.K. Babbar• Dr. Ramji Rai

• Dr. R.G. Sharma• Mr. R.B. Saxena• Dr. Ratan Lal• Dr. B.V. Reddi• Mr. S.S. Verma• Dr. S.K. Agarwal• Dr. P.L. Upadhyay• Dr. Anurag Gupta• Mr. M.A. Ansari• Mr. Ashok Kumar• Dr. V.P.S. Awana• Mr. P.K. Dutta• Mr. S.B. Samanta• Mr.U.C. Upreti

• Dr. Hari Kishan

Structure of the Talk

About NPL [very briefly]Cryogenics & Low Temperature Physics: Past,Present & Future activitiesHumidity: its generation, control andmeasurement [very briefly]Superconductivity: Past & Recent activity

NATIONAL PHYSICAL LABORATORY, NEW DELHI

Established in 1946, inaguarated in 1950One of the 38 laboratories of CSIRNational Metrology InstituteAbout 1000 staff membersOne of the premier institutes of IndiaTo maintain standards of highest accuracyTo do research in physics based areas such as Low Temp. Physics/Cryogenics, Material Research & Radio Science

R&D Divisions of NPL

Physico-MechanicalStandards

Electrical & ElectronicsStandards

NPLRadio & AtmosphericSciences

Cryogenics &Superconductivity

Engineering Materials

Electronic Materials

Materials Characterization

EARLIER WORK [1950-1970]

• Low Temp. Physics/Cryogenics started in 1952• India’s first liquid helium plant 4 litres/hour• ADL electromagnet producing ~ 2 tesla field• Unique facilities, provided boost to researchers• de Haas van-Alfen effect in Bi crystals• Electrical resistivity, thermal conductivity,

MR, thermal expansion, specific heat, magnetic susceptibility on metals & very dilute magnetic alloys (Kondo system)

CRYO-SURGERY

LIQUIDNITROGEN/

HELIUMVESSELS/

CRYOSTATS

MINIATUREJ.T.

CRYO-COOLERS

SUPERCONDUCTINGMAGNETS

HTSCSTUDIES

BASIC SUPERCONDUCTIVITY

A 15 TYPESUPERCONDUCTORS

TAPES

KONDO EFFECT

TRANSPORT PROPERTIES

THEORYGROUP

Cryogenics&

Superconductivity

PRESERVATIONSYSTEM FOR

CONSTITUTIONOF INDIA

ICE

LINED

REFRIGERATOR

HELIUM

PURITY

MONITOR

CRYOGENIC

TEMPERATURE

CONTROLLERLIQUID NITROGEN

LEVEL DETECTORS &

TRANSFER PUMPS HYDRIDE

COOLERS

CRYOGENIC FACILITY

HUMIDITY

MEASUREMENTS

CRYO-ACCESSORIES

• Air liquefiers based on Linde and Stirling cycles

• Liquid nitrogen level indicators and controller• Low evaporation loss rate super-insulated

container (20 ltrs capacity)• Cryogenic Temperature Controller• Helium Purity Monitor

CAPACITANCE TYPE LIQUID LEVEL SENSOR

• The difference in the dielectric constant of liquid and vapour phases is the basis of this sensor

• Liquid level is a linear function of the capacitance of the gauge

• Sensitivity is independent of the length of the probe or the liquid level

• One of the most accurate sensors • It can very easily be made in the

laboratory• The electrodes consist of two

concentric stainless steel tubes

THERMODYNAMIC LIQUID-LEVEL GAUGE

• It is based on the principle that a liquid undergoes a large change in volume when it is evaporated

• Pressure within the dead volume is the indication of the liquid level

• Simplest to fabricate in the laboratory

• Very well suited for the operators• Does not require any electricity to

operate• Gives an approximate amount of

liquid in the vessel• Sensor is a thin stainless steel

capillary tube

ELECTRIC RESISTANCE BASED LIQUID-LEVEL INDICATORS

• Heat transfer coefficient for a liquid is much higher compared to that of vapour

• Measurement of electrical resistance of a heated wire (with a small electric current) can indicate interface between liquid and its vapour

• Two types of indicators based on this method are possible (1) movable resistor and (2) fixed resistance type which gives a continuous level indication

Liquid Nitrogen Transfer Pump

• A submersible centrifugal type liquid nitrogen transfer pump

• A discharge capacity of about 5 liter /minute of liquid nitrogen

• The pump can be fitted on a cryogenic container with an inside neck diameter of 40 mm or more and with a depth down to 900 mm from top of the neck to the bottom of the inner vessel.

• The impeller is made in brass and has a diameter of 35 mm. It rotates at a speed of 3000-4000 rpm.

Superinsulated Cryogenic Vessels & Cryostats

• Developed super insulated cryo-containers• Capacity = 20 litres, double walled in aluminium with

FRP neck• Evaporation rate = 0.32 litres/day, [1.6%]• Multilayers of 9 microns thick aluminium foil &

Dexter fibre glass paper & high vacuum• Large size liquid nitrogen container (250 litres) using

perlite insulation, having evaporation rate ~ 5%/day• Long hold LHe cryostat (~195 litres) with RT bore of

52 mm, evaporation rate of 0.7% and a holdover time of 90 days

Thermal conductivity of various insulations

Developed test facility for the measurement of apparent thermal conductivity of various types of insulation such as powder, fibrous and multi-layer between the two boundary temperatures of 77K and 300 K with varying densities & pressuresAim was to help indian industries

Cryo-surgical units for medical applications

• Joule-Thomson based Cryo-surgical units for medical applications using nitrous oxide gas as refrigerant, were developed

• Machine was tested for ophthalmology area- for cataract removal, retinal detachment & glaucoma [temp range –30 to 60 C], ENT area [-70 to –80C]

• Developed high refrigeration capacity Cryo-probes, needed for the destruction of benign & malignant tumors in the head, throat, nasal and neck area

Miniature J.T. Cryocoolers for IR Devices (77-80 K)

• During late 80s a project was undertaken & completed for the development of Joule Thomson based cryocoolers (77-80K0 for T.R. detectors

• Cryocoolers are very compact & fast action type• It has dimensions of 7.22±0.01 mm dia & 25 mm

length of heat exchanger, working at 4000 to 6000 pst nitrogen gas

• Cool down time to 77-80 K is of 1-2 minutes

ICE-LINED REFRIGERATORS (125 & 275 LITRES CAPACITY) FOR STORING LIFE SAVING VACCINES

It has three compartmentsNo. 1: + 4oC ± 2oCNo. 2: - 4oC ± 2oCNo. 3: -15oC ± 2oC

Ambient Hold Over Temperature Time

32oC 72 Hours26oC 118 Hours20oC 200 Hours

AS PER WHO NORMS, HOLD OVER TIME SHOULD BE ATLEAST 40 HOURS

SPECIAL ICE-LINED REFRIGERATOR(275 litres capacity)

Hydrogen-Hydride Cooling Device

• Feasibility studies on hydrogen-hydride cooling device: DST funded project

• In collaboration with BHU, Prof. ON Srivastava• Materials synthesized at BHU• Heat reactors & cooling device fabricated, tested

and demonstrated successfully to DST experts• Because of high cost of materials did not come in

the commercial market

Development of a Test Rig for Cryogenic ValvesA Consultancy Project from M/s Leader Engineering Works, Jalandhar,

Test Rig developed for Cryogenic Valves for carrying out leak tests up to 25 Bar as per BS : 6364.

Assembly comprises of a) cooling coil, b) FRP tank for liquid nitrogen, c) control valves and d) flow meter.

Capable of checking leak rate for gate valves / check valves in sizes ranging from DN25 to DN 300.

Leak rate tests at different pressure and temperature done for a typical DN 150 gate valve.

Cryogenic Valve Test Set-up

PRESERVATION OF THE ORIGINAL MANUSCRIPT OF THE CONSTITUTION OF INDIA

Two bound calligraphic volumes in English and HindiDimensions 45 (L) x 8 (B) x 60 (H) Cms; Weight ` 14 Kgms250 sheets of hand made parchment paper in each volumeThese have great autographic as well as historical value, as they contain the signatures of the founding fathers of the Constitution

Long Term Preservation of Indian Constitution (Earlier Work)

To develop suitable glass receptacles for viewing purposesTo store the documents in an inert gas atmosphereTo maintain RH 45±5% & Temperature 20 ±2oC inside theglass receptacle containing inert gasTo decrease O2 concentration of less than 1% by volume

Case sealed by soldering Case sealed by O-ring

Collaboration with the Getty Conservation Institute, USA

Two display cases with O’ring seal were developedHanded over the complete system on 27th October 1995Developed RH generation system, that gave birth to a new activity in the laboratory [Humidity Standard]Periodic monitoring of O2 & RH inside the display casesBased on our measurement of O2 leak rate, it is estimated that

these cases can be maintained at <2% O2 concentration for 10 years and 20 years with oxygen scavanger inside the display cases

DIVIDED/MIXED/TWO FLOW RH GENERATOR

TWO-PRESSURE RH GENERATOR

PORTABLE RELATIVE HUMIDITY GENERATOR

• BASED ON “TWO-PRESSURE” PRINCIPLE

• MOST ACCURATE AND RELIABLE

• INDIGENOUS• FILED INDIAN PATENT• 10 – 95% RH RANGE• ± 1% RH ACCURACY• ACCURACY DEPENDS ON

PRECISE MEASUREMENT OF TEMP. & PRESSURE

• SELF CONTAINED FACILITY

MINI RELATIVE HUMIDITY GENERATOR

• SIMPLE, VERSATILE AND COMPACT DEVICE

• RH RANGE 10-95%• - 10 To + 25oC DEW POINT

TEMPERATURE• ±1 % RH ACCURACY• LIGHT WEIGHT• NEEDS ONLY THE GAS

SOURCE (AIR OR N2)• EXTREMELY USEFUL FOR

ONSITE CALIBRATION IN THE INDUSTRY

• EXCELLENT, TRACEABLE & FUNDAMENTAL METHODFILED INDIAN PATENT

2P+ 2T GENERATOR

Two-Pressure cum Two-Temperature RH Generator

Uncertainty

±0.07oC in DP&

±0.5 % in RH

Dew Point Range: -30 to +60oC ; RH Range: 3 to 98 %

SUPERCONDUCTIVITY & CRYOGENICS

SUPERCONDUCTIVITY• HTSC materials• Sodium Cobaltate• Ruthenocuprates• Magnesium diboride• Theoretical studies

CRYOGENICS• SC magnets• Cryostats• Inserts• Cryogenic infra-

structural facility

EXISTING FACILITIES

CLOSED CYCLE REFRIGERATORSAC SUSCEPTOMETER (ACS7000)TGA / DTASTM /AFMSUPERCONDUCTING MAGNETSHIGH TEMPERATURE FURNACESHUMIDITY GENERATION, CONTROL & MEASUREMENTCRYOGENIC PLANTS & WORKSHOP

Resistivity measurement set up down to 12K

Insert Type 3.5 T Insert Type 3.5 T SuperconductingSuperconducting MagnetMagnet

Working bore 28 mmNo need of special cryostatLow liquid helium consumptionVery compact and light weightEconomical

Field homogeneity over 10 mm DSV is 0.12 %

0

1

2

3

4

-10 -5 0 5 10

DISTANCE ( CM )

FIE

LD (

T )

Insert Type 3.5 T Insert Type 3.5 T SuperconductingSuperconducting MagnetMagnet

1.14 Kg1.14 KgTotal weightTotal weight

796 J796 JTotal stored energyTotal stored energy

±0.12%±0.12%Field HomogeneityField Homogeneity99879987Total turnsTotal turns

0.285 mm0.285 mmConductor Conductor –– Cu/Cu/NbNb--TiTi

120 mm120 mmWinding LengthWinding Length

53.7 mm53.7 mmOuter Winding Outer Winding DiaDia..

34.6 mm34.6 mmInner Winding Inner Winding DiaDia..

28 mm28 mmWorking Bore Working Bore DiaDia

VALUEVALUEPARAMETERSPARAMETERS

Room Temperature Bore Cryostat for NMR ApplicationsRoom Temperature Bore Cryostat for NMR Applications

RT bore : 52 mmRT bore : 52 mm

LHeLHe capacity: 190 capacity: 190 ltrsltrs

SuperinsulationSuperinsulation : NRC: NRC--22

He evaporation rate : 1.35 l/dayHe evaporation rate : 1.35 l/day

7 Tesla 7 Tesla SuperconductingSuperconducting MagnetMagnet

Field : 7 T in 50 mm boreField : 7 T in 50 mm bore

Field homogeneity : 0.07 % over Field homogeneity : 0.07 % over 10 mm DSV10 mm DSV

Design optimized for field Design optimized for field homogeneity, current density and low homogeneity, current density and low peak fieldpeak field

Magnet wound in two sectionsMagnet wound in two sections

Dump resistors are provided for Dump resistors are provided for quench protectionquench protection

VapourVapour cooled current leadscooled current leads

Cryostats for 7 T Cryostats for 7 T Superconducting Superconducting MagnetsMagnets

Support systemSupport system : Top : Top flange, supporting flange, supporting tubes/rods, radiation tubes/rods, radiation baffles, baffles, LHeLHe fill tube & fill tube & level sensorlevel sensor

CryostatsCryostats : Cylindrical, : Cylindrical, double walled and double walled and superinsulated superinsulated Capacity : 25 Capacity : 25 ltrsltrsPressure relief valvePressure relief valveHelium gas recovery portHelium gas recovery port

Development of 11 Tesla Development of 11 Tesla SuperconductingSuperconducting MagnetMagnet

The outer coil (The outer coil (NbNb--Ti) wound in Ti) wound in two sections. two sections.

The inner section with MF The inner section with MF Cu/Cu/NbTiNbTi wire (0.75 mm wire (0.75 mm diadia) )

Outer section with MF Cu/Outer section with MF Cu/NbTiNbTiwire (0.54 mm wire (0.54 mm diadia).).

The insert coil of NbThe insert coil of Nb33Sn wound Sn wound & reacted for 120hrs at 570& reacted for 120hrs at 57000C C and 80 hrs at 700and 80 hrs at 70000C in argon C in argon atmosphere.atmosphere.

Both the coils were vacuum Both the coils were vacuum impregnated with bees wax.impregnated with bees wax.

Development of 11 Tesla Development of 11 Tesla SuperconductingSuperconducting MagnetMagnet

The two coils have The two coils have been first tested been first tested individually and then individually and then combined. combined.

The magnet has been The magnet has been successfully tested up successfully tested up to 11.1 T. to 11.1 T.

Large Bore, 6 Tesla Large Bore, 6 Tesla SuperconductingSuperconducting MagnetMagnetA Collaborative Project with Institute for Plasma Research, A Collaborative Project with Institute for Plasma Research, GandhinagarGandhinagar

Bore Bore diadia. ~255mm. ~255mmWinding length ~ 556mmWinding length ~ 556mmCu/Cu/NbNb--Ti wire of 0.56mm Ti wire of 0.56mm diadia..One old lathe machine for One old lathe machine for winding such a large size coil winding such a large size coil was modified.was modified.A suitable wire A suitable wire tensionertensioner to to handle the heavy spool was handle the heavy spool was fabricated.fabricated.The SC magnet coil has 42 The SC magnet coil has 42 layers with ~ 1000 turns in each layers with ~ 1000 turns in each layerlayer

This is one of the largest indigenously fabricated Superconducting Magnet

CRYO INFRA-STRUCTURE FACILITY

44 44 litreslitres per hr capacity per hr capacity StirLinStirLin--4 4 liquid nitrogen plant6000 litres LN2 Vessel liquid nitrogen plant

DESIGN OF CRYOGEN–FREE 5 T SC MAGNET

• Use closed cycle refrigerator for cooling

• HTSC leads to cut down heat load

• RT Bore : 50 mm, • Inner Winding dia.= 102 mm• Field 5 T at 100 A • Homogeneity of 0.1% over 10

mm DSV• Cu/NbTi wire dia: 0.75 mm

α= 1.65 and β-=1.8• Total Layers = 38

High Field SC Magnet

Why Sodium Cobaltate

Two fold interest

Good thermoelectric material

Becomes superconductor withthe intercalation of water

NaxCoO2 [x = 1.0, 0.7 & 0.6]

• Figure of Merit: Z = (S2/ρκ) ≅ 1 ; [Bi2Te3]• It is believed that good electrical conduction

is ensured by CoO2 block & high thermo-electric power is contributed from Na-Ophonon drag layer

• κ = 10-15 mW/cmK in temps. 5-400K range• Power factor, P = (S2/ρ) • Magnetic structure is complex & the exact

arrangement of Co spins is yet unclear

H. Kishan et al

Journal of Applied Physics 97, 10A904 (2005)

Results on Sodium Cobaltate

• Synthesized NaxCoO2 with x = 1.0, 0.7 & 0.6 system• Measured resistivity & thermoelectric power from

room temperature down to 12K• S(at 300K) ≅ 80, 39 & 37 µV/K • ρ (300K) ~ 0.895 mΩcm for x = 1.0• Power factor (S2 / ρ) ~ 7.04x10-3 W/mK2

• Qualifies it as a good thermoelectric material• Samples with x =1.0 & 0.7 are metallic down to 5K,

while x = 0.6 is semi-conducting• Anomalous S(T) for x = 0.70 and 0.60 samples

Why rutheno-cuprates: Motivation

Traditional theories of superconductivity ruleout the coexistence of sc and magnetismRuthenocuprates are a class of HTSC materials that show coexistence of sc (Tc) & magnetism (Tmag), that behave like super-conducting ferromagnets with Tmag > Tc

To study the correlation of Tc and Tmag by replacing Ru partially by other ions of magnetic (Co, Fe) or nonmagnetic (Nb, Mo)

THREE RECENT PUBLICATIONS ON RUTHENOCUPRATES

Magnetism, upper critical field and thermoelectricpower of RuSr2Eu1.5Ce0.5Cu2O10-δ

J. Phys.: Condens. Matter 18, 1-9 (2006)Experimental study of RuSr2Eu1.5Ce0.5Cu2O10-δ :

Effect of Mo doping on magnetic behaviour and Tcvariation [Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10-δ]

Physical Review B 73, 014517 (2006)Impact of Co & Mo substitution at Ru site in

RuSr2Eu1.5Ce0.5Cu2O10-δ magnetosuperconductorMod. Phys. Lett. B.(2006)

RESULTS OF RuSr2Eu1.5Ce0.5Cu2O10-δ

• Susceptibility measurements show magnetic orderbelow 140K (Tmag) and a superconducting transition at 25K (Tc)

• ρ shows a metallic behaviour between 75 and 140K, weestimated a mean free path of 56Å at zero Kelvin

• Upper critical field shows a positive curvature and corresponds to a minimum of 32T at T= 0 K

• A narrow-band approach (Gasumyants et al) is found to explain the observed thermoelectric power above 100 K in terms of two parameters, µ and W0 (energy width); µ = 8.0 meV and W0 = 58.5 meV

WHY MgB2?

• Simple crystal structure (hexagonal AlB2 type)• Larger coherence length• Lower anisotropy, simple to synthesize• High critical temperature (Tc = 39K), inexpensive• Nearly transparent grain boundaries permitting

excellent current flow• Possibility of improving pinning centres• High energy ion irradiation, oxygen alloying,

chemical doping using different elements & nano-particle addition are routes to improve high Jc

MgB2 Synthesis Path

Quartz Tube

Soft Iron Tube

Mg and B powder are properly mixed in the stoichiometric ratio of 1:2, and pelletized.

Pellet was sealed at soft iron tube and it is subsequently sealed into quartz tube in vacuum of order 10-5 mbar.

Encapsulated MgB2 was heated at 750ºC for various of holding time.

The ampoule is directly quenched at LN2 by breaking quartz tube inside liquid.

Vacuum Inside: 10 -5 m bar

R-T Measurement

0 50 100 150 200 2500.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

Tc~38K

MgB2(NPL)

17-02-2005Fe-Tube-7500C2 hours,10/20 gain1 hr hold

R (Ω

)

T (K)0 50 100 150 200

0.000

0.005

0.010

0.015

Tc ~ 30K

TSG(K) 50 K

MgB2 (NPL) Ist4-02-2005Fe-Tube-800 0C2 hours, 20/30 gain R

(Ω)

T (K)

NATIONAL PHYSICAL LABORATORY

0 35 70 105 140 175 210 245

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

Tc~38K

MgB2(Slow cooling in furnace)750oC 1:30hr holdGain 3021/3/2005

R (Ω

)

T ( K)0 50 100 150 2000.0

2.0x10-4

4.0x10-4

6.0x10-4

8.0x10-4

1.0x10-3

1.2x10-3

1.4x10-3

1.6x10-3

1.8x10-3

Tc = 38.78 K

MgB2 750oC

gain 30, 2:30 hr hold28-03-2005R(

Ω)

T(K)

K.P. Singh et al

Mod. Phys. Lett. B (2006)

The nano-Co3O4 added MgB2:Sup. Science & Technology (2006)

0 10 20 30 40 50

-0.09

-0.06

-0.03

0.00χ

(em

u/g)

T (K)

MgB2 + nano Co3O4

0, 2, 4 and 6% H = 5 Oe

FC

ZFC

0 50 100 150 200 250

0

50

100

150

200 MgB2 + Nano Co3O4

ρ

(µΩ

-cm

)

T (K)

Pure MgB2 2% Co3O4 4% Co3O4 6% Co3O4

20 30 40 50 60 70

0

2000

4000

6000

I (ar

b. u

nits

)

2 (θ) Degrees

MgB2 + nano Co3O4

x = 0.0

x = 0.02

x = 0.06

(010

) (100

)

Mg

(101

)

(002

) (110

)(M

gO)

(102

)(1

11)

Co2O3

x = 0.04

MgB2 samples with 0, 2, 4 and 6% added nano-Co3O4 (particle size 20nm) samples were synthesized by encapsulation of well mixed and pelletized high quality Mg, B and nano-Co3O4 powders in a soft Fe-tube and its subsequent heating to 750 0C for two and half hours in an evacuated (10-5 Torr) quartz tube and quenching to liquid-nitrogen temperature.

M(H) and Jc of nano-Co3O4 MgB2

-6 -4 -2 0 2 4 6

-400

-200

0

200

400

M(e

mu/

cm3 )

H (Tesla)

MgB2 PureT = 5, 10, 20, 25, 30 and 35 K

-6 -4 -2 0 2 4 6-900

-600

-300

0

300

600

900

M (e

mu/

cm3 )

H (Tesla)

MgB2+ 2% nano Co3O4

T = 5, 10, 20, 25, 30 K, 35 K

Fluxiod Jumps region

0 1 2 3 4 5 6 7

105

106

107

108 MgB2 + nano Co3O4

0, 2, 4 and 6% T = 5, 10, 20, 30 K

J c (A/c

m2 )

H (Tesla)

Fluxiod Jumps region

2%

4%0%6%

comparison of the ρ behaviour of MgB2, AlB2 & AgB2 systems

• Synthesized samples of MgB2 , AlB2 and AgB2

• Measured their resistivity from 300 K down to 12K

• Combined effect of impurity scattering, electron-phonon interaction (Bloch-Gruneisen theory) andweak localization provides a reasonable explanationof the resistivity data

Result of ρ comparison of different borides

MgB2a = 3.08 Åc = 3.51 Å

AlB2a = 3.01 Åc = 3.24 Å

AgB2a = 2.88 Åc = 3.53 Å

Bloch-Gruneisen Theory

First term gives the temperature independent contributionto resistivity due to impurities. Second term arises due to contribution of the electron-phonon interaction withinBloch-Gruneisen theory, here A is a constant independentof T & Debye temperature. Third term is contribution dueto weak localization, where B is a constant. The constant A provides contribution of the electron-phonon interaction, while the constant B provides contribution of weaklocalization.

From the values of ρo and A it appears that effect of impurities andelectron-phonon interaction is maximum in AlB2, while it is least inAgB2 sample. From the value of B, contribution of weak localizationIs absent in MgB2; it is 20 times larger in AlB2 compared to AgB2. This is consistent with the values of ρo values for these two samples,because ρo (AlB2) is about 22 times larger than ρo (AgB2).

θD(MgB2) > θD(AlB2) > θD(AgB2) ; since one of the factors on whichθD depends is the mass of the constituent atoms , and sincemass(Mg) < mass(Al) < mass(Ag), it may be argued that the atoms ofMg, Al and Ag make essential contribution in determining θD.

R. Lal, V.P.S. Awana, H. Kishan & A.V. Narlikar Mod. Phys. Lett. B (2006)

Collaborations & Projects

• UGC project on basic superconductivity

• Indo-Israel project from DST

• BHU (Prof. ONS)• TIFR (Prof. SK

Malik)• IISc (Prof. DD Sarma)• IUAC, Indore (Dr. AV

Narlikar)

• UNICAMP, Brasil• University of Sao-

Carlos, Brasil• NIMS, Japan• University of Turku,

Finland• Tokyo Institute of

Technilogy, Japan• University of Racah,

Jerusalem

ICC (North Zone) announces the holding of

XXI [Twenty first National Symposium on Cryogenics] at National Physical Laboratory, New Delhi from 22nd to 24th November 2006 as a part of NPL’s diamond Jubilee celebrations.This is as per decision in the last ICC General Body Meeting held at Surat.

(Hari Kishan) (R.B. Saxena)Jt. Convenor Convenor

THANK YOU