Materials Chemistry and Physics50 (1997) 57-62 Growth and characterization of amino acids mixed triglycine sulpho-phosphate single crystals G. Arunmozhi, R. Jayavel, C. Subramanian * Crystal Growth Centre, Ama Universi@, Madras 600 025, India Received 13 September 1996; revised 15 January 1997 Abstract The growth of amino acids mixed triglycine sulpho-phosphate (TGSP) crystals has been investigated. The crystals were grown by a slow cooling technique. The amino acids mixed were I-alanine (ATGSP), 1-valine (VTGSP), I-asparagine ( ASP-TGSP)and 1-arginine (ARG- TGSP), the structure of these amino acids are similar to glycine. Changes in the morphology of the crystals with substitution havebeen identified. Thepresence of amino acids in thecrystalhas been identified by FTIR analysis. Therelative permittivity decreases in thecase of asparagine mixed TGSP crystal (ASP-TGSP).Powder X-ray diffractionshows changes in thepeak positions and relative intensity for amino acids mixedTGSP crystals. Keywords: Amino acids: Triglycine sulpho-phosphate; Mixed crystals 1. Introduction Triglycine sulphate (TGS) is a good pyroelectric material that can be usedfor room temperature pyroelectric detection in the rangeof 2-18 p,m because of its low dielectric constant and high pyroelectric coefficient. The transition temperature of TGS is 49°C [ 1,2]. It belongs to the monoclinic system with space group P2, in the ferroelectric phase andP2, lm in the paraelectric phase.Spontaneous polarization takesplace along the ferroelectric b-axis. Partial substitution of sulphate with phosphate has resulted in triglycine sulpho-phosphate (TGSP) crystal, which has T, at 51°C [3]. The b-plane is wider in TGSP which can be used for the fabrication of pyroelectric detectors [ 41. The dielectric permittivity is also low for TGSP compared with TGS [ 51. The lattice parameter values of TGSP are a = 9.15 A, b = 12.69 A, c =5.73 A and cell volume 665.3 A’. The pyroelectric figure of merit (pl E’ ) , demands low permittivity andhigh pyroelectric coef- ficient. Substitution of alanine in the place of glycine has improved the ferroelectric properties. Alanine mixed TGS ( ATGS) remains permanently poled single domain crystal [ 6-101. Amino acids mixed TGS have been widely studied and reported [ 111. The amino acids mixed TGS have low permittivity values compared with pure TGS. In the present investigation the amino acids I-valine, I-alanine, 1-asparagine * Corresponding author. 0254-0584/97/$17,00 0 1997 Elsevier Science S.A. All rights reserved PllSO254-0584(97)01906-8 and I-arginine have been substituted in the TGSP lattice in order to improve the pyroelectric figure of merit of TGSP. The amino acids chosen have similar structure to glycine. 2. Crystal growth Triglycine sulpho-phosphate (TGSP) was synthesised according to the reaction 3 (NH,CH,COOH) + .uH,SO, + ( 1 -x) H,PO, * (NH,CH,COOH) 3 . (H,SO,), . (H,POJ 1 -.r where x = 0.5. Analar grade glycine, sulphuric acid and phos- phoric acid were used in this synthesis. To the saturated solution of TGSP, the amino acid was mixed until the solution became saturated with respect to the amino acid added. The equilibrium concentration of these amino acidsat 40°C was 2.7 g in 100 ml of saturated TGSP solution. The pH of the solution was 2.3. The saturated solu- tion has been filtered with a 0.2 p,rn porosity nuclear filter. The solution was maintained at 50°C for 24 h before seeding. Inclusion-free spontaneously nucleated seeds were sus- pended from the stirrer in the solution. Crystal growth was carried out by slow cooling until the crystals grew to a con- siderable size, An optically heated crystallizer with a con- trolling accuracy of k O.Ol”C was used for the growth. The temperature reduction was in the range O.l-0.25”C day- ’ as