research papers J. Appl. Cryst. (2019). 52, 1371–1377 https://doi.org/10.1107/S1600576719013797 1371 Received 26 April 2019 Accepted 9 October 2019 Edited by F. Meilleur, Oak Ridge National Laboratory, USA, and North Carolina State University, USA Keywords: neutron diffraction; hydrogen bonding; crystal growth; interionic interactions. CCDC references: 1958605; 1963870 Supporting information: this article has supporting information at journals.iucr.org/j a-Nickel sulfate hexahydrate crystals: relationship of growth conditions, crystal structure and properties R. R. Choudhury, a * R. Chitra, a I. P. Makarova, b V. L. Manomenova, b E. B. Rudneva, b A. E. Voloshin b and M. V. Koldaeva b a Solid State Physics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400085, India, and b Shubnikov Institute of Crystallography of Federal Scientific Research Centre ‘Crystallography and Photonics’ of Russian Academy of Sciences, Leninskii prospekt 59, Moscow 119333, Russian Federation. *Correspondence e-mail: rajulranjan@gmail.com Studies on -nickel sulfate hexahydrate (NSH) crystals grown under different conditions are undertaken to investigate how changes in growth conditions affect crystal properties and whether or not there is any modification of the average crystal structure due to changes in crystallization conditions. Thermo- gravimetric and microhardness studies were carried out on the crystals grown from two different aqueous solutions, one of them containing an excess of sulfuric acid. Raman spectra were recorded and a single-crystal neutron diffraction investigation was conducted on both crystals. A detailed comparison between the two crystal structures and their Raman spectra showed that, although the two crystal structures are very similar, there are slight differences, such as the change in unit-cell volume, differences in the ionic structure, particularly of the sulfate ions, and changes in the hydrogen-bonding network. During solution crystal growth of a salt like NSH, varying the ionic environment around the solute ions influences the interionic interactions between them. Hence it is suggested that the above-mentioned structural differences result from a fine-tuning of the interionic interaction between the cations and anions of NSH in the solution phase. This difference is finally carried over to the crystalline phase. The resulting small crystal structure differences are enough to produce measurable changes in the thermal stability and fragility of the crystals. These differences in crystal properties can be explained on the basis of the observed structural differences between the two crystals grown under different conditions. 1. Introduction Crystals form an integral part of modern day technology, particularly our electronics industry. The photonics industry depends heavily on crystal growth technology; hence there has been a steadily growing interest in recent times in crystal growth processes (Bombicz et al., 2014). In order to achieve high performance from a device, good quality single crystals are needed. A crystal is not formed instantaneously; initial ordering, i.e. nucleation, occurs at first in a disordered phase, followed by growth, during which growth conditions and thus growth rates, forms, degrees of perfection and homogeneities change. Each crystal has its own growth history, and the external and internal imperfection and inhomogeneity of a crystal is the result and record of that growth history (Suna- gawa, 1999). In order to grow good quality single crystals, it is important to know how crystal growth conditions affect crystals externally as well as internally. In this article we have undertaken a study on -nickel sulfate hexahydrate (NSH) crystals grown under slightly different conditions in order to ISSN 1600-5767 # 2019 International Union of Crystallography