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JOURNAL OF MATERIALS SCIENCE LETTERS 5 (1986) 989-990Preparation of zinc phosphideK . R . M U R A L I , B . S . V . G O P A L A MDepartment of Physics, Indian institute of Technology, Madras-600 036, India

Zn3P2 has recent ly ga ined impor tance owing to i t sposs ib le use in photo vol ta ic devices [1 , 2] . Al l previo usinves t iga t ions have been on mate r ia l s synthes ized byd i r e ct r e a c t ion o f z i nc a nd phos p hor us . T he s em a t e r i a l s e xh i b i t e d p - t ype c onduc t i v i t y w h i c h ha sbeen a t t r ibu ted to the presence of na t ive defec t s(phosphorous in te rs t i t i a l s ) .

I n ou r l a bo r a t o r y Z n3P 2 w a s p r e pa r e d by t he c a r -b o n r e d u c t io n o f p u r e zi nc o r t h o p h o s p h a t e . T w ovar ie t i es of Zn3 (P04) 2 were used as the s t a r t ing chemi-c a l . I n one c a s e , z i nc dus t a nd o r t hophos phor i c a c i d ,bo t h o f A na l a r g r a de qua l i t y , w e r e u se d . I n t he o t he rc a se , A na l a r g r a de Z nO a nd H 3 P O 4 w e r e u s ed . U s i ngbo t h t he se m a t e r i a l s , Z n3 P 2 w a s p r e pa r e d by a c a r bo nr e duc t i on p r oc e s s ( u s i ng s pe c pu r e c a r bon ) a t t e m -pe r a t u r e s a r oun d 600 C . W h e r e a s t he y i e l d o f Z n3P 2w a s poo r f o r f i r i ng t e m p e r a t u r e s l ow e r t ha n 600 C ,

G a s i n l e tJ;T e m p e r a t u r e /c o n t r o e r [

I . . . . . . . . 1/ = < 3 = =

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Figure 1 Schematic diagram o f the vacuum furnace

I 150(ill

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"0----.__I l I -~-4 8 12 16Duration of reaction { h)

Figure 2 TSL output plotted against reac-tion time.0261-8028/86 $03.0 0 + .12 1986 Chapman and Hall Ltd. 9 8 9

7/28/2019 Murali.gopalam.preparation.of.Zinc.phosphide

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I ]30 40 I I I I50 60 70 802 e ( deg)

Figure 3 X-ray diffractogram of Zn3P2.

material loss occurred above 600C in a vacuum(10 3torr) furnace for different times between 2 and16. The product obtained from both types ofZn3(PO4)2 exhibited similar properties.The material studied in this investigation wasprepared by thoroughly grinding a mixture of 3.8 gpure Zn3(PO4) 2 and 1.6g specpure carbon in a pul-verizer. The powder was then transferred to an aluminaboat which was subsequently heated in a vacuumfurnace. After completion of the heat treatment thesamples were quenched to room temperature by blow-ing cold air over them for about 5 min. A schematicdiagram of the tubular vacuum furnace designed forthis purpose is shown in Fig. l. A facility has beenprovided in the furnace for heating the samples undervacuum, as well as in an inert atmosphere.

Materials obtained by this method after continuingthe reaction for 16 h in vacuum have exhibited onlythe prominent lines of Zn 3P2- Zn3 P2 was also preparedby carbon reduction of Zn3(PO4)2 in air and the yieldof Zn3P2 was very poor; it also contained someunreacted Zn3(PO4)2, and so only the mater ialprepared under vacuum/inert atmosphere was usedas starting material for crystal growth and filmpreparation.We have established the duration of the reaction bystudying the thermally stimulated luminescence (TSL)of samples taken from the furnace after differentreaction times. These samples were exposed to X rays(30kV, 10mA, 10rain) and their TSL glow curveswere compared with those of pure Zn3(PO4)2. Theglow curves exhibited glow peaks in almost the sametemperature regions for durations less than 8hbecause of the presence of unreduced Zn3(PO4)2 andZn3 P2.As the reaction proceeds beyond 8 h the TSL ou tput

also decreases. The TSL output proportional to thearea under the glow curve is plotted against time ofreaction in Fig. 2. For the material (Zn3P2) obtainedafter allowing the reduction process to continue forperiods greater than 15h no TSL output could bedetected, even after operat ing the detector in the veryhigh sensitivity range.The X-ray diffractogram obtained using CuK~radiation on materials obtained after continuing thereduction process beyond 15h indicated only thesharp lines assignable to ~-Zn3P2. The X-raydiffractograms are shown in Fig. 3.The material obtained by the above process wasfinally ground to a uniform particle size of 75 #m andwas then used as starting material for obtaining thinfilms of Zn3P2 on glass substrates by thermal evapor-ation. Some of the results on electrical properties havealready been published [3-5]. Further work on thepreparation of crystals and epitaxial films is inprogress.R e f e r e n c e s1. J. M. PAWLIKOWSKI, in "Proceedings of the Inter-national Conference on the Physics and Chemistry of II V

Comp ound s," Mogilany, 1980, edited by M. J. Gelten andL. Zdanowicz (Ein dhoven University of Technology, 1981)p. 157.

2. A. CATALANO, V. DALAL, E. A. FAGEN, R. B.HALL, G. WARFIELD and A. M. BARNETT, Proceedings ofthe 1 t EC Photovoltaic Solar Energy Conference, Luxembourg,September 1977 (Reidel, Dordrecht, Boston, 1978) p. 644.

3. K. R. MU RAL I and D. R. RAO, J. Mater. Sei . 16 (1981)547.

4. Idem, J. Mater. SeL Let t . 1 (1982) 383.5. Idem, Thin Sol id Fi lms 86 (1982) 283.

Received 28 Februaryand accepted 17 April 1986

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